Encoder, decoder, encoding method, and decoding method

ABSTRACT

An encoder which encodes image information includes memory and circuitry accessible to the memory. The circuitry binarizes a data value indicating the number of non-zero coefficients included in a current basic block which is one of one or more basic blocks in a frequency transform block, according to a conversion table, to encode the image information which includes the data value. When binarizing the data value, the circuitry selects the conversion table from a plurality of tables including two or more tables which differ from each other in difference between a longest bit length and a shortest bit length of a plurality of binary values associated with a plurality of data values, according to the position of the current basic block in the current frequency transform block which is the frequency transform block including the current basic block, and binarizes the data value according to the conversion table selected.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application of PCT InternationalPatent Application Number PCT/JP2017/028397 filed on Aug. 4, 2017,claiming the benefit of priority of U.S. Patent Application No.62/373,010 filed on Aug. 10, 2016, the entire contents of which arehereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to an encoder which encodes imageinformation, and to others.

2. Description of the Related Art

In H.265 (ISO/IEC 23008-2 HEVC (High Efficiency Video Coding)) which isa conventional encoding method, image information including frequencytransform coefficient information related to frequency components of animage is encoded.

SUMMARY

However, the coding amount of frequency transform coefficientinformation significantly affects the total coding amount of imageinformation. Accordingly, if the frequency transform coefficientinformation is not appropriately processed, the total coding amount ofthe image information may increase.

In view of this, the present disclosure provides an encoder capable ofappropriately processing frequency transform coefficient information,and so on.

An encoder according to an aspect of the present disclosure is anencoder which encodes image information, the encoder including: memory;and circuitry accessible to the memory, wherein the circuitry accessibleto the memory: binarizes a data value indicating the number of non-zerocoefficients included in a current basic block which is one of one ormore basic blocks in a frequency transform block composed of a pluralityof frequency transform coefficients, according to a conversion table inwhich a plurality of data values and a plurality of binary values areassociated with each other, to encode the image information whichincludes the data value; and when binarizing the data value, selects theconversion table from a plurality of tables including two or more tableswhich differ from each other in difference between a longest bit lengthand a shortest bit length of a plurality of binary values associatedwith the plurality of data values, according to a position of thecurrent basic block in the current frequency transform block which isthe frequency transform block including the current basic block, andbinarizes the data value according to the conversion table selected.

These general and specific aspects may be implemented using a system, anapparatus, a method, an integrated circuit, a computer program, or acomputer-readable recording medium such as a CD-ROM, or any combinationof systems, apparatuses, methods, integrated circuits, computerprograms, or computer-readable recording media.

The encoder, etc. according to an aspect of the present disclosureenables appropriate processing of frequency transform coefficientinformation.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram illustrating a functional configuration of anencoder according to Embodiment 1.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1.

FIG. 3 is a chart indicating transform basis functions for eachtransform type.

FIG. 4A illustrates one example of a filter shape used in ALF.

FIG. 4B illustrates another example of a filter shape used in ALF.

FIG. 4C illustrates another example of a filter shape used in ALF.

FIG. 5 illustrates 67 intra prediction modes used in intra prediction.

FIG. 6 is for illustrating pattern matching (bilateral matching) betweentwo blocks along a motion trajectory.

FIG. 7 is for illustrating pattern matching (template matching) betweena template in a current picture and a block in a reference picture.

FIG. 8 is for illustrating a model assuming uniform linear motion.

FIG. 9 is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks.

FIG. 10 is a block diagram illustrating a functional configuration of adecoder according to Embodiment 1.

FIG. 11 is a block diagram illustrating a specific functionalconfiguration of an entropy encoder in an encoder according toEmbodiment 1.

FIG. 12 is a block diagram illustrating a specific functionalconfiguration of an entropy decoder in a decoder according to Embodiment1.

FIG. 13 is a flowchart indicating a syntax structure according toEmbodiment 1.

FIG. 14A is a conceptual diagram of a basic block in a 4×4 frequencytransform block according to Embodiment 1.

FIG. 14B is a conceptual diagram of basic blocks in an 8×8 frequencytransform block according to Embodiment 1.

FIG. 14C is a conceptual diagram of basic blocks in an 8×4 frequencytransform block according to Embodiment 1.

FIG. 14D is a conceptual diagram of basic blocks in a 4×8 frequencytransform block according to Embodiment 1.

FIG. 14E is a conceptual diagram of basic blocks in a 16×16 frequencytransform block according to Embodiment 1.

FIG. 14F is a conceptual diagram of basic blocks in a 16×8 frequencytransform block according to Embodiment 1.

FIG. 14G is a conceptual diagram of basic blocks in an 8×16 frequencytransform block according to Embodiment 1.

FIG. 14H is a conceptual diagram of basic blocks in a 16×12 frequencytransform block according to Embodiment 1.

FIG. 14I is a conceptual diagram of basic blocks in a 4×16 frequencytransform block according to Embodiment 1.

FIG. 15 is a conceptual diagram indicating two kinds of tables accordingto Embodiment 1.

FIG. 16 is a flowchart indicating selection of a table according toEmbodiment 1.

FIG. 17 is a conceptual diagram indicating four kinds of tablesaccording to Embodiment 1.

FIG. 18A is a conceptual diagram of a basic block layer in a 4×4frequency transform block according to Embodiment 1.

FIG. 18B is a conceptual diagram of a basic block layer in an 8×8frequency transform block according to Embodiment 1.

FIG. 18C is a conceptual diagram of a basic block layer in an 8×4frequency transform block according to Embodiment 1.

FIG. 18D is a conceptual diagram of a basic block layer in a 4×8frequency transform block according to Embodiment 1.

FIG. 18E is a conceptual diagram of basic blocks in a 16×16 frequencytransform block according to Embodiment 1.

FIG. 18F is a conceptual diagram of basic blocks in a 16×8 frequencytransform block according to Embodiment 1.

FIG. 18G is a conceptual diagram of basic blocks in an 8×16 frequencytransform block according to Embodiment 1.

FIG. 18H is a conceptual diagram of basic blocks in a 16×12 frequencytransform block according to Embodiment 1.

FIG. 18I is a conceptual diagram of basic blocks in a 4×16 frequencytransform block according to Embodiment 1.

FIG. 19 is a flowchart indicating a pattern determination processingaccording to Embodiment 1.

FIG. 20A is a conceptual diagram illustrating a current basic blockhaving a first pattern according to Embodiment 1.

FIG. 20B is a conceptual diagram illustrating a current basic blockhaving a second pattern according to Embodiment 1.

FIG. 20C is a conceptual diagram illustrating a current basic blockhaving a third pattern according to Embodiment 1.

FIG. 21 is a relationship diagram indicating tables to be selected inthe first pattern according to Embodiment 1.

FIG. 22 is a relationship diagram indicating tables to be selected inthe second pattern according to Embodiment 1.

FIG. 23 is a relationship diagram indicating tables to be selected for aneighboring frequency transform block in the third pattern according toEmbodiment 1.

FIG. 24 is a relationship diagram indicating tables to be selected inthe coding mode in the third pattern according to Embodiment 1.

FIG. 25 is a relationship diagram indicating tables to be selected basedon quantization parameters in the third pattern according to Embodiment1.

FIG. 26 is a data diagram indicating a syntax structure according toEmbodiment 1.

FIG. 27 is a block diagram illustrating a mounting example of theencoder according to Embodiment 1.

FIG. 28 is a flowchart indicating an example of a first encodingoperation performed by the encoder according to Embodiment 1.

FIG. 29 is a flowchart indicating binarization processing in the exampleof the first encoding operation performed by the encoder according toEmbodiment 1.

FIG. 30 is a flowchart indicating binarization processing of frequencytransform coefficient information in the example of the first encodingoperation performed by the encoder according to Embodiment 1.

FIG. 31 is a flowchart indicating an example of a second encodingoperation performed by the encoder according to Embodiment 1.

FIG. 32 is a flowchart indicating an example of a third encodingoperation performed by the encoder according to Embodiment 1.

FIG. 33 is a flowchart indicating binarization processing in the exampleof the third encoding operation performed by the encoder according toEmbodiment 1.

FIG. 34 is a flowchart indicating binarization processing in an exampleof a fourth encoding operation performed by the encoder according toEmbodiment 1.

FIG. 35 is a block diagram illustrating a mounting example of thedecoder according to Embodiment 1.

FIG. 36 is a flowchart indicating an example of a first decodingoperation performed by the decoder according to Embodiment 1.

FIG. 37 is a flowchart indicating inverse binarization processing in theexample of the first decoding operation performed by the decoderaccording to Embodiment 1.

FIG. 38 is a flowchart indicating inverse binarization processing of abinary data string of frequency transform coefficient information in theexample of the first decoding operation performed by the decoderaccording to Embodiment 1.

FIG. 39 is a flowchart indicating an example of a second decodingoperation performed by the decoder according to Embodiment 1.

FIG. 40 is a flowchart indicating an example of a third decodingoperation performed by the decoder according to Embodiment 1.

FIG. 41 is a flowchart indicating inverse binarization processing in theexample of the third decoding operation performed by the decoderaccording to Embodiment 1.

FIG. 42 is a flowchart indicating inverse binarization processing in theexample of the fourth decoding operation performed by the decoderaccording to Embodiment 1.

FIG. 43 illustrates an overall configuration of a content providingsystem for implementing a content distribution service.

FIG. 44 illustrates one example of an encoding structure in scalableencoding.

FIG. 45 illustrates one example of an encoding structure in scalableencoding.

FIG. 46 illustrates an example of a display screen of a web page.

FIG. 47 illustrates an example of a display screen of a web page.

FIG. 48 illustrates one example of a smartphone.

FIG. 49 is a block diagram illustrating a configuration example of asmartphone.

DETAILED DESCRIPTION OF THE EMBODIMENTS Underlying Knowledge FormingBasis of the Present Disclosure

In H.265 which is a conventional encoding method, arithmetic encoding isused to encode image information efficiently. Specifically, acontext-based adaptive binary arithmetic coding method referred to asCABAC is employed.

For example, in the context-based adaptive binary arithmetic codingmethod, multi-value signals are converted, by binarization, into abinary data string which is a data string in which each of values arerepresented as 0 or 1. According to context such as a data type, or thelike, an occurrence probability of 0 or 1 is selected from a pluralityof predetermined occurrence probabilities, and binary arithmeticencoding is applied to the binary data string according to the selectedoccurrence probability. The occurrence probability is updated accordingto the value of 0 or 1 included in the binary data string.

In other words, in the context-based adaptive binary arithmetic codingmethod, binary arithmetic encoding is performed according to a variableoccurrence probability. In addition, in the context-based adaptivebinary arithmetic coding method, data having a particular data type, orthe like is binary arithmetic encoded according to a fixed occurrenceprobability.

Furthermore, in H.265, image information including frequency transformcoefficient information is encoded. The frequency transform coefficientinformation is information related to frequency components of an image,and is suitable for processing such as encoding and decoding of theimage. However, the coding amount of the frequency transform coefficientinformation significantly affects the total coding amount of the imageinformation. Accordingly, if the frequency transform coefficientinformation is not appropriately encoded, the total coding amount of theimage information may increase.

In view of this, an encoder according to an aspect of the presentdisclosure is an encoder which encodes image information and outputs abitstream in which the image information has been encoded, the encoderincluding: memory; and circuitry accessible to the memory, wherein thecircuitry accessible to the memory: binarizes the image information;switches whether or not to apply arithmetic encoding to a binary datastring in which the image information has been binarized; whenarithmetic encoding is applied to the binary data string, appliesarithmetic encoding to the binary data string, and outputs the bitstreamwhich includes the binary data string to which arithmetic encoding hasbeen applied; when arithmetic encoding is not applied to the binary datastring, skips applying arithmetic encoding to the binary data string,and outputs the bitstream which includes the binary data string to whicharithmetic encoding has not been applied; when binarizing the imageinformation, binarizes frequency transform coefficient information whichis related to frequency components of an image and included in the imageinformation, according to different binarization formats between whenarithmetic encoding is applied to the binary data string and whenarithmetic encoding is not applied to the binary data string; and whenbinarizing the image information, binarizes a part or an entirety ofprediction parameter information which is related to prediction methodsof the image and included in the image information, according to acommon binarization format between when arithmetic encoding is appliedto the binary data string and when arithmetic encoding is not applied tothe binary data string.

In this way, the encoder is capable of skipping arithmetic encoding,Accordingly, the encoder is capable of supporting reduction inprocessing delay generated by arithmetic encoding. Furthermore, theencoder is capable of appropriately binarizing the frequency transformcoefficient information which significantly affects the total codingamount, according to the binarization formats which are differentdepending on whether or not arithmetic encoding is applied. Accordingly,the encoder is capable of appropriately encoding the frequency transformcoefficient information, thereby being able to reduce increase in thetotal coding amount.

For example, the circuitry may binarize at least one of the followingkinds of information included in the prediction parameter information:information related to coding modes, information related to predictiondirections in intra prediction, information related to referencepictures in inter prediction, and information related to motion vectorsin inter prediction, according to the common binarization format betweenwhen arithmetic encoding is applied to the binary data string and whenarithmetic encoding is not applied to the binary data string.

In this way, the encoder is capable of efficiently binarizing the atleast part of information included in the prediction parameterinformation according to the common binarization format.

For example, the circuitry may binarize the following kinds ofinformation included in the prediction parameter information:information related to coding modes, information related to predictiondirections in intra prediction, information related to referencepictures in inter prediction, and information related to motion vectorsin inter prediction, according to the common binarization format betweenwhen arithmetic encoding is applied to the binary data string and whenarithmetic encoding is not applied to the binary data string.

In this way, the encoder is capable of efficiently binarizing thevarious kinds of information included in the prediction parameterinformation according to the common binarization format.

In addition, for example, when binarizing the image information, thecircuitry may binarize only the frequency transform coefficientinformation in the image information according to the differentbinarization formats, and may binarize all information other than thefrequency transform coefficient information in the image informationaccording to the common binarization format.

In this way, the encoder is capable of binarizing all of the informationother than the frequency transform coefficient information, according tothe common binarization format. Accordingly, the processing issimplified.

In addition, for example, when binarizing the image information, thecircuitry may binarize the frequency transform coefficient informationaccording to a format which generates a smaller number of bits whenarithmetic encoding is not applied to the binary data string than whenarithmetic encoding is applied to the binary data string.

In this way, the encoder is capable of assisting reduction in codingamount of the frequency transform coefficient information whenarithmetic encoding is not applied.

Furthermore, a decoder according to an aspect of the present disclosureis a decoder which obtains a bitstream in which image information hasbeen encoded and decodes the image information, the decoder including:memory; circuitry accessible to the memory, wherein the circuitryaccessible to the memory: obtains the bitstream which includes a binarydata string in which the image information has been binarized; switcheswhether or not to apply arithmetic decoding to the binary data stringincluded in the bitstream; when arithmetic decoding is applied to thebinary data string, applies arithmetic decoding to the binary datastring, and inverse binarizes the binary data string to which arithmeticdecoding has been applied, to decode the image information; whenarithmetic decoding is not applied to the binary data string, skipsapplying arithmetic decoding to the binary data string, and inversebinarizes the binary data string to which arithmetic decoding has notbeen applied, to decode the image information; when inverse binarizingthe binary data string, inverse binarizes a first portion which isincluded in the binary data string and in which frequency transformcoefficient information related to frequency components of an image hasbeen binarized, according to different inverse binarization formatsbetween when arithmetic decoding is applied to the binary data stringand when arithmetic decoding is not applied to the binary data string;and when inverse binarizing the binary data string, inverse binarizes asecond portion which is included in the binary data string and in whicha part or an entirety of prediction parameter information related toprediction methods of an image has been binarized, according to a commoninverse binarization format between when arithmetic decoding is appliedto the binary data string and when arithmetic decoding is not applied tothe binary data string.

In this way, the decoder is capable of skipping arithmetic decoding.Accordingly, the decoder is capable of supporting reduction inprocessing delay generated by the arithmetic decoding. Furthermore, thedecoder is capable of appropriately inverse binarizing the first portionin which the frequency transform coefficient information whichsignificantly affects the total coding amount has been binarized,according to whether or not arithmetic decoding is applied. Accordingly,the decoder is capable of appropriately decoding the frequency transformcoefficient information, thereby being able to reduce increase in thetotal coding amount.

For example, the circuitry may inverse binarize the second portion inwhich at least one of the following kinds of information included in theprediction parameter information has been binarized: information relatedto coding modes; information related to prediction directions in intraprediction; information related to reference pictures in interprediction; and information related to motion vectors in interprediction, according to the common inverse binarization format betweenwhen arithmetic decoding is applied to the binary data string and whenarithmetic decoding is not applied to the binary data string.

In this way, the decoder is capable of efficiently inverse binarizingthe portion in which the at least part of information included in theprediction parameter information has been binarized, according to thecommon inverse binarization format.

In addition, for example, the circuitry may inverse binarize the secondportion in which the following kinds of information included in theprediction parameter information have been binarized: informationrelated to coding modes, information related to prediction directions inintra prediction, information related to reference pictures in interprediction, and information related to motion vectors in interprediction, according to the common inverse binarization format betweenwhen arithmetic decoding is applied to the binary data string and whenarithmetic decoding is not applied to the binary data string.

In this way, the decoder is capable of efficiently inverse binarizingthe portion in which the various kinds of information included in theprediction parameter information has been binarized, according to thecommon inverse binarization format.

In addition, for example, when inverse binarizing the binary datastring, the circuitry may inverse binarize only the first portion in thebinary data string according to the different inverse binarizationformats, and may inverse binarize all information other than the firstportion in the binary data string according to the common inversebinarization format.

In this way, the decoder is capable of inverse binarizing all of theportion other than the first portion in which the frequency transformcoefficient information has been binarized, according to the commoninverse binarization format. Accordingly, the processing is simplified.

In addition, for example, when inverse binarizing the binary datastring, the circuitry may inverse binarize the first portion in whichthe frequency transform coefficient information has been binarizedaccording to a format which generates a smaller number of bits whenarithmetic decoding is not applied to the binary data string than whenarithmetic decoding is applied to the binary data string.

In this way, the decoder is capable of assisting reduction in codingamount of the frequency transform coefficient information whenarithmetic decoding is not applied.

Furthermore, an encoding method according to an aspect of the presentdisclosure is an encoding method for encoding image information andoutputting a bitstream in which the image information has been encoded,the encoding method including: binarizing the image information;switching whether or not to apply arithmetic encoding to a binary datastring in which the image information has been binarized; whenarithmetic encoding is applied to the binary data string, applyingarithmetic encoding to the binary data string, and outputting thebitstream which includes the binary data string to which arithmeticencoding has been applied; when arithmetic encoding is not applied tothe binary data string, skipping applying arithmetic encoding to thebinary data string, and outputting the bitstream which includes thebinary data string to which arithmetic encoding has not been applied; inthe binarizing of the image information, binarizing frequency transformcoefficient information which is related to frequency components of animage and included in the image information, according to differentbinarization formats between when arithmetic encoding is applied to thebinary data string and when arithmetic encoding is not applied to thebinary data string; and in the binarizing of the image information,binarizing a part or an entirety of prediction parameter informationwhich is related to prediction methods of the image and included in theimage information, according to a common binarization format betweenwhen arithmetic encoding is applied to the binary data string and whenarithmetic encoding is not applied to the binary data string.

In this way, the apparatus, etc. which performs the encoding method iscapable of skipping arithmetic encoding. Accordingly, the apparatus,etc. which performs the encoding method is capable of supportingreduction in processing delay generated by the arithmetic encoding.Furthermore, the apparatus, etc. which performs the encoding method iscapable of appropriately binarizing the frequency transform coefficientinformation which significantly affects the total coding amount,according to the binarization formats which are different depending onwhether or not arithmetic encoding is applied. Accordingly, theapparatus, etc. which performs the encoding method is capable ofappropriately encoding the frequency transform coefficient information,thereby being able to reduce increase in the total coding amount.

Furthermore, a decoding method according to an aspect of the presentdisclosure is a decoding method for obtaining a bitstream in which imageinformation has been encoded and decoding the image information, thedecoding method including: obtaining the bitstream which includes abinary data string in which the image information has been binarized;switching whether or not to apply arithmetic decoding to the binary datastring included in the bitstream; when arithmetic decoding is applied tothe binary data string, applying arithmetic decoding to the binary datastring, and inverse binarizing the binary data string to whicharithmetic decoding has been applied, to decode the image information;when arithmetic decoding is not applied to the binary data string,skipping applying arithmetic decoding to the binary data string, andinverse binarizing the binary data string to which arithmetic decodinghas not been applied, to decode the image information; in the inversebinarizing of the binary data string, inverse binarizing a first portionwhich is included in the binary data string and in which frequencytransform coefficient information related to frequency components of animage has been binarized, according to different inverse binarizationformats between when arithmetic decoding is applied to the binary datastring and when arithmetic decoding is not applied to the binary datastring; and in the inverse binarizing of the binary data string, inversebinarizing a second portion which is included in the binary data stringand in which a part or an entirety of prediction parameter informationrelated to prediction methods of an image has been binarized, accordingto a common inverse binarization format between when arithmetic decodingis applied to the binary data string and when arithmetic decoding is notapplied to the binary data string.

In this way, the apparatus, etc. which performs the decoding method iscapable of skipping arithmetic decoding. Accordingly, the apparatus,etc. which performs the decoding method is capable of supportingreduction in processing delay generated by the arithmetic decoding.Furthermore, the apparatus, etc. which performs the decoding method iscapable of appropriately inverse binarizing the first portion in whichthe frequency transform coefficient information which significantlyaffects the total coding amount has been binarized, according to whetheror not arithmetic decoding is applied. Accordingly, the apparatus, etc.which performs the decoding method is capable of appropriately decodingthe frequency transform coefficient information, thereby being able toreduce increase in the total coding amount.

Furthermore, an encoder according to an aspect of the present disclosuremay be an encoder which encodes image information, the encoderincluding: memory; and circuitry accessible to the memory, wherein thecircuitry accessible to the memory: encodes position informationindicating a position of a specific basic block which is a basic blockincluding a non-zero coefficient first in a predetermined scan orderdefined in a descending order of frequencies of one or more basic blocksincluded in a frequency transform block composed of a plurality offrequency transform coefficients; and encodes only block informationindicating a plurality of frequency transform coefficients of each ofthe specific basic block and a following basic block in thepredetermined scan order.

In this way, the encoder is capable of binarizing the positioninformation and the block information as the frequency transformcoefficient information. Since the encoder encodes the block informationof each of the specific basic block and the following basic block in thepredetermined scan order, the encoder is capable of assisting reductionin the coding amount of the frequency transform coefficient information.

For example, the circuitry may encode the position information only whenthe number of the one or more basic blocks is two or more.

In this way, when, for example, the size of the frequency transformblock and the size of each basic block is the same, the encoder iscapable of assisting further reduction in coding amount of the frequencytransform coefficient information.

In addition, for example, the circuitry may encode the positioninformation and the block information only when the specific basic blockis present in the frequency transform block.

In this way, when, for example, no non-zero coefficient is included inthe frequency transform block, the encoder is capable of assistingfurther reduction in coding amount of the frequency transformcoefficient information.

In addition, for example, the circuitry: may encode the imageinformation, and may output a bitstream in which the image informationhas been encoded; when encoding the image information and outputting thebitstream: may binarize the image information; may switch whether or notto apply arithmetic encoding to a binary data string in which the imageinformation has been binarized; when arithmetic encoding is applied tothe binary data string, may apply arithmetic encoding to the binary datastring, and may output the bitstream which includes the binary datastring to which arithmetic encoding has been applied; and whenarithmetic encoding is not applied to the binary data string, may skipapplying arithmetic encoding to the binary data string and may outputthe bitstream which includes the binary data string to which arithmeticencoding has not been applied, and when binarizing the imageinformation, may binarize frequency transform coefficient informationwhich is related to frequency components of an image and included in theimage information, according to different binarization formats betweenwhen arithmetic encoding is applied to the binary data string and whenarithmetic encoding is not applied to the binary data string; whenbinarizing the image information, may binarize a part or an entirety ofprediction parameter information which is related to prediction methodsof an image and included in the image information, according to a commonbinarization format between when arithmetic encoding is applied to thebinary data string and when arithmetic encoding is not applied to thebinary data string; and when binarizing the frequency transformcoefficient information in the case where arithmetic encoding is notapplied to the binary data string, may binarize the frequency transformcoefficient information including the position information and the blockinformation, to encode the position information and the blockinformation.

In this way, the encoder is capable of assisting reduction in codingamount of the frequency transform coefficient information whenarithmetic encoding is not applied.

Furthermore, a decoder according to an aspect of the present disclosuremay be a decoder which decodes image information, the decoder including:memory; and circuitry accessible to the memory, wherein the circuitryaccessible to the memory: decodes position information indicating aposition of a specific basic block which is a basic block including anon-zero coefficient first in a predetermined scan order defined in adescending order of frequencies of one or more basic blocks included ina frequency transform block composed of a plurality of frequencytransform coefficients; and decodes only block information indicating aplurality of frequency transform coefficients of each of the specificbasic block and a following basic block in the predetermined scan order.

In this way, the decoder is capable of decoding the position informationand the block information as the frequency transform coefficientinformation. Since the decoder decodes the block information of each ofthe specific basic block and the following basic block in thepredetermined scan order, the decoder is capable of assisting reductionin the coding amount of the frequency transform coefficient information.

For example, the circuitry may decode the position information only whenthe number of the one or more basic blocks is two or more.

In this way, when, for example, the size of the frequency transformblock and the size of each basic block is the same, the encoder iscapable of assisting further reduction in coding amount of the frequencytransform coefficient information.

In addition, for example, the circuitry may decode the positioninformation and the block information only when the specific basic blockis present in the frequency transform block.

In this way, when, for example, no non-zero coefficient is included inthe frequency transform block, the decoder is capable of assistingfurther reduction in coding amount of the frequency transformcoefficient information.

In addition, for example, the circuitry: may obtain a bitstream in whichthe image information has been encoded, and may decode the imageinformation; when obtaining the bitstream and decoding the imageinformation: may obtain the bitstream which includes a binary datastring in which the image information has been binarized; may switchwhether or not to apply arithmetic decoding to the binary data stringwhich is included in the bitstream; when arithmetic decoding is appliedto the binary data string, may apply arithmetic decoding to the binarydata string, and may inverse binarize the binary data string to whicharithmetic decoding has been applied, to decode the image information;and when arithmetic decoding is not applied to the binary data string,may skip applying arithmetic decoding to the binary data string, and mayinverse binarize the binary data string to which arithmetic decoding hasnot been applied, to decode the image information; when inversebinarizing the binary data string, may inverse binarize a first portionwhich is included in the binary data string and in which frequencytransform coefficient information related to frequency components of animage has been binarized, according to different inverse binarizationformats between when arithmetic decoding is applied to the binary datastring and when arithmetic decoding is not applied to the binary datastring; when inverse binarizing the binary data string, may inversebinarize a second portion which is included in the binary data stringand in which a part or an entirety of prediction parameter informationrelated to prediction methods of the image has been binarized, accordingto a common inverse binarization format between when arithmetic decodingis applied to the binary data string and when arithmetic decoding is notapplied to the binary data string; and when inverse binarizing the firstportion in the case where arithmetic decoding is not applied to thebinary data string, may inverse binarize the first portion in which thefrequency transform coefficient information including the positioninformation and the block information has been binarized, to decode theposition information and the block information.

In this way, the decoder is capable of assisting reduction in codingamount of the frequency transform coefficient information whenarithmetic decoding is not applied.

Furthermore, an encoding method according to an aspect of the presentdisclosure may be an encoding method for encoding image information, theencoding method including: encoding position information indicating aposition of a specific basic block which is a basic block including anon-zero coefficient first in a predetermined scan order defined in adescending order of frequencies of one or more basic blocks included ina frequency transform block composed of a plurality of frequencytransform coefficients; and encoding only block information indicating aplurality of frequency transform coefficients of each of the specificbasic block and a following basic block in the predetermined scan order.

In this way, the apparatus, etc. which performs the encoding method iscapable of encoding the position information and the block informationas the frequency transform coefficient information. Since the apparatus,etc. which performs the encoding method encodes the block information ofeach of the specific basic block and the following basic block in thepredetermined scan order, the encoder is capable of assisting reductionin the coding amount of the frequency transform coefficient information.

Furthermore, a decoding method according to an aspect of the presentdisclosure may be a decoding method for decoding image information, thedecoding method including: decoding position information indicating aposition of a specific basic block which is a basic block including anon-zero coefficient first in a predetermined scan order defined in adescending order of frequencies of one or more basic blocks included ina frequency transform block composed of a plurality of frequencytransform coefficients; and decoding only block information indicating aplurality of frequency transform coefficients of each of the specificbasic block and a following basic block in the predetermined scan order.

In this way, the apparatus, etc. which performs the decoding method iscapable of decoding the position information and the block informationas the frequency transform coefficient information. Since the apparatus,etc. which performs the decoding method decodes the block information ofeach of the specific basic block and the following basic block in thepredetermined scan order, the decoder is capable of assisting reductionin the coding amount of the frequency transform coefficient information.

Furthermore, an encoder according to an aspect of the present disclosuremay be an encoder which encodes image information, the encoderincluding: memory; and circuitry accessible to the memory, wherein thecircuitry accessible to the memory: binarizes a data value indicatingthe number of non-zero coefficients included in a current basic blockwhich is one of one or more basic blocks in a frequency transform blockcomposed of a plurality of frequency transform coefficients, accordingto a conversion table in which a plurality of data values and aplurality of binary values are associated with each other, to encode theimage information which includes the data value; and when binarizing thedata value, selects the conversion table from a plurality of tablesincluding a first table which includes association with a data valueindicating 0 as the number of non-zero coefficients and a second tablewhich does not include association with a data value indicating 0 as thenumber of non-zero coefficients, and binarizes the data value accordingto the conversion table selected.

In this way, the encoder is capable of appropriately encoding theinformation for efficiently representing the plurality of frequencytransform coefficients which constitute the basic block. In addition,the encoder is capable of using the table having a reduced informationamount as the conversion table for binarization. Accordingly, theencoder is capable of assisting reduction in coding amount of thefrequency transform coefficient information.

For example, when binarizing the binary value, the circuitry maybinarize, as the data value indicating the number of non-zerocoefficients included in a current basic block, a data value indicatingthe number of non-zero coefficients included in only each of a specificbasic block and a following basic block in a scan order defined as adescending order of frequencies of the one or more basic blocks, thespecific basic block being a basic block including a non-zerocoefficient first in the one or more basic blocks.

In this way, the encoder is capable of assisting reduction in codingamount of the frequency transform coefficient information.

In addition, for example, the circuitry: when binarizing the data value,may binarize the data value only when the specific basic block ispresent in the one or more basic blocks; and when selecting theconversion table, may select the second table as the conversion tablewhen the frequency transform block and the current basic block areidentical.

In this way, when, for example, the size of the frequency transformblock and the size of each basic block are the same, the encoder iscapable of assisting further reduction in coding amount of the frequencytransform coefficient information, using the second table which does notinclude any association with a data value indicating 0 as the number ofnon-zero coefficients.

In addition, for example, the circuitry, when selecting the conversiontable, may select the second table as the conversion table when thecurrent basic block is the specific basic block.

In this way, when, for example, the current basic block is a specificbasic block, the encoder is capable of assisting further reduction incoding amount of the frequency transform coefficient information, usingthe second table which does not include any association with a datavalue indicating 0 as the number of non-zero coefficients.

In addition, for example, the circuitry: may encode the imageinformation, and may output a bitstream in which the image informationhas been encoded; when encoding the image information and outputting thebitstream: may binarize the image information; may switch whether or notto apply arithmetic encoding to a binary data string in which the imageinformation has been binarized; when arithmetic encoding is applied tothe binary data string, may apply arithmetic encoding to the binary datastring, and may output the bitstream which includes the binary datastring to which arithmetic encoding has been applied; and whenarithmetic encoding is not applied to the binary data string, may skipapplying arithmetic encoding to the binary data string and may outputthe bitstream which includes the binary data string to which arithmeticencoding has not been applied, and when binarizing the imageinformation, may binarize frequency transform coefficient informationwhich is related to frequency components of an image and included in theimage information, according to different binarization formats betweenwhen arithmetic encoding is applied to the binary data string and whenarithmetic encoding is not applied to the binary data string; whenbinarizing the image information, may binarize a part or an entirety ofprediction parameter information which is related to prediction methodsof an image and included in the image information, according to a commonbinarization format between when arithmetic encoding is applied to thebinary data string and when arithmetic encoding is not applied to thebinary data string; and when binarizing the frequency transformcoefficient information in the case where arithmetic encoding is notapplied to the binary data string, may binarize the data value includedin the frequency transform coefficient information, according to theconversion table selected from the plurality of tables including thefirst table and the second table.

In this way, when arithmetic encoding is not applied, the encoder iscapable of assisting reduction in coding amount of the frequencytransform coefficient information, using the conversion table selectedfrom the plurality of tables including the second table which does notinclude any association with a data value indicating 0 as the number ofnon-zero coefficients.

Furthermore, a decoder according to an aspect of the present disclosuremay be a decoder which decodes image information, the decoder including:memory; and circuitry accessible to the memory, wherein the circuitryaccessible to the memory: inverse binarizes a binary value which hasbeen obtained by binarizing a data value according to a conversion tablein which a plurality of data values and a plurality of binary values areassociated with each other, to decode the image information whichincludes the data value, the data value indicating the number ofnon-zero coefficients included in a current basic block which is one ofone or more basic blocks in a frequency transform block composed of aplurality of frequency transform coefficients; and when inversebinarizing the data value, selects the conversion table from a pluralityof tables including a first table which includes association with a datavalue indicating 0 as the number of non-zero coefficients and a secondtable which does not include association with a data value indicating 0as the number of non-zero coefficients, and inverse binarizes the binaryvalue according to the conversion table selected.

In this way, the decoder is capable of appropriately decoding theinformation for efficiently representing the plurality of frequencytransform coefficients which constitute the basic block. In this way,the decoder is capable of using the table having a reduced informationamount as the conversion table for inverse binarization. Accordingly,the decoder is capable of assisting reduction in coding amount of thefrequency transform coefficient information.

For example, when inverse binarizing the binary value, the circuitry maybinarize, as a binary value obtained by binarizing the data valueindicating the number of non-zero coefficients included in a currentbasic block, a binary value obtained by binarizing a data valueindicating the number of non-zero coefficients included in only each ofa specific basic block and a following basic block in a scan orderdefined as a descending order of frequencies of the one or more basicblocks, the specific basic block being a basic block including anon-zero coefficient first in the one or more basic blocks.

In this way, the decoder is capable of assisting reduction in codingamount of the frequency transform coefficient information.

In addition, for example, the circuitry: when inverse binarizing thebinary value, may inverse binarize the binary value only when thespecific basic block is present in the one or more basic blocks; andwhen selecting the conversion table, may select the second table as theconversion table when the frequency transform block and the currentbasic block are identical.

In this way, when, for example, the size of the frequency transformblock and the size of each basic block are the same, the decoder iscapable of assisting further reduction in coding amount of the frequencytransform coefficient information, using the second table which does notinclude any association with a data value indicating 0 as the number ofnon-zero coefficients.

In addition, for example, the circuitry, when selecting the conversiontable, may select the second table as the conversion table when thecurrent basic block is the specific basic block.

In this way, when, for example, the current basic block is the specificbasic block, the decoder is capable of assisting further reduction incoding amount of the frequency transform coefficient information, usingthe second table which does not include any association with a datavalue indicating 0 as the number of non-zero coefficients.

In addition, for example, the circuitry: may obtain a bitstream in whichthe image information has been encoded, and may decode the imageinformation; when obtaining the bitstream and decoding the imageinformation: may obtain the bitstream which includes a binary datastring in which the image information has been binarized; may switchwhether or not to apply arithmetic decoding to the binary data stringwhich is included in the bitstream; when arithmetic decoding is appliedto the binary data string, may apply arithmetic decoding to the binarydata string, and may inverse binarize the binary data string to whicharithmetic decoding has been applied, to decode the image information;and when arithmetic decoding is not applied to the binary data string,may skip applying arithmetic decoding to the binary data string, and mayinverse binarize the binary data string to which arithmetic decoding hasnot been applied, to decode the image information; when inversebinarizing the binary data string, may inverse binarize a first portionwhich is included in the binary data string and in which frequencytransform coefficient information related to frequency components of animage has been binarized, according to different inverse binarizationformats between when arithmetic decoding is applied to the binary datastring and when arithmetic decoding is not applied to the binary datastring; when inverse binarizing the binary data string, may inversebinarize a second portion which is included in the binary data stringand in which a part or an entirety of prediction parameter informationrelated to prediction methods of the image has been binarized, accordingto a common inverse binarization format between when arithmetic decodingis applied to the binary data string and when arithmetic decoding is notapplied to the binary data string; and when inverse binarizing the firstportion in the case where arithmetic decoding is not applied to thebinary data string, may inverse binarize the binary value included inthe first portion, according to the conversion table selected from theplurality of tables including the first table and the second table.

In this way, when arithmetic decoding is not applied, the decoder iscapable of assisting reduction in coding amount of the frequencytransform coefficient information, using the conversion table selectedfrom the plurality of tables including the second table which does notinclude any association with a data value indicating 0 as the number ofnon-zero coefficients.

Furthermore, an encoding method according to an aspect of the presentdisclosure may be an encoding method for encoding image information, theencoding method including: binarizing a data value indicating the numberof non-zero coefficients included in a current basic block which is oneof one or more basic blocks in a frequency transform block composed of aplurality of frequency transform coefficients, according to a conversiontable in which a plurality of data values and a plurality of binaryvalues are associated with each other, to encode the image informationwhich includes the data value; and in the binarizing of the data value,selecting the conversion table from a plurality of tables including afirst table which includes association with a data value indicating 0 asthe number of non-zero coefficients and a second table which does notinclude association with a data value indicating 0 as the number ofnon-zero coefficients, and binarizing the data value according to theconversion table selected.

In this way, the apparatus, etc. which performs the encoding method iscapable of appropriately encoding the information for efficientlyrepresenting the plurality of frequency transform coefficients whichconstitute the basic block. In addition, the apparatus, etc. whichperforms the encoding method is capable of using the table having areduced information amount as the conversion table for binarization.Accordingly, the apparatus, etc. which performs the encoding method iscapable of assisting reduction in coding amount of the frequencytransform coefficient information.

In addition, a decoding method according to an aspect of the presentdisclosure may be a decoding method for decoding image information, thedecoding method including: inverse binarizing a binary value which hasbeen obtained by binarizing a data value according to a conversion tablein which a plurality of data values and a plurality of binary values areassociated with each other, to decode the image information whichincludes the data value, the data value indicating the number ofnon-zero coefficients included in a current basic block which is one ofone or more basic blocks in a frequency transform block composed of aplurality of frequency transform coefficients: and in the inversebinarizing of the data value, selecting the conversion table from aplurality of tables including a first table which includes associationwith a data value indicating 0 as the number of non-zero coefficientsand a second table which does not include association with a data valueindicating 0 as the number of non-zero coefficients, and inversebinarizing the binary value according to the conversion table selected.

In this way, the apparatus, etc. which performs the decoding method iscapable of appropriately decoding the information for efficientlyrepresenting the plurality of frequency transform coefficients whichconstitute the basic block. In addition, the apparatus, etc. whichperforms the decoding method is capable of using the table having areduced information amount as the conversion table for inversebinarization. Accordingly, the apparatus, etc. which performs thedecoding method is capable of assisting reduction in coding amount ofthe frequency transform coefficient information.

Furthermore, an encoder according to an aspect of the present disclosuremay be an encoder which encodes image information, the encoderincluding: memory; and circuitry accessible to the memory, wherein thecircuitry accessible to the memory: binarizes a data value indicatingthe number of non-zero coefficients included in a current basic blockwhich is one of one or more basic blocks in a frequency transform blockcomposed of a plurality of frequency transform coefficients, accordingto a conversion table in which a plurality of data values and aplurality of binary values are associated with each other, to encode theimage information which includes the data value; and when binarizing thedata value, selects the conversion table from a plurality of tablesincluding two or more tables which differ from each other in differencebetween a longest bit length and a shortest bit length of a plurality ofbinary values associated with the plurality of data values, according toa position of the current basic block in the current frequency transformblock which is the frequency transform block including the current basicblock, and binarizes the data value according to the conversion tableselected.

In this way, the encoder is capable of appropriately encoding theinformation for efficiently representing the plurality of frequencytransform coefficients which constitute the basic block. In this way,the encoder is capable of selecting the conversion table for binarizingthe data value indicating the number of non-zero coefficients, accordingto the position of the current basic block. The characteristics of thenumber of non-zero coefficients differ depending on the position of thecurrent basic block. Accordingly, the encoder is capable of reflectingthe characteristic of the number of non-zero coefficients in theselection of the conversion table, using the position of the currentbasic block. Accordingly, the encoder is capable of appropriatelyselecting the conversion table, and assisting reduction in coding amountof the frequency transform coefficient information.

For example, when selecting the conversion table, the circuitry mayselect the conversion table according to the number of non-zerocoefficients included in a preceding basic block which is a basic blocklocated before the current basic block in a predetermined scan orderdefined in a descending order of frequencies of the one or more basicblocks in the case where the preceding basic block is present at thesame frequency level as a frequency level at the position of the currentbasic block.

In this way, the encoder is capable of selecting the conversion tableaccording to the non-zero coefficients of the preceding basic blockwhich is estimated to have a similar number of non-zero coefficientswith respect to the number of non-zero coefficients of the current basicblock.

In addition, for example, when selecting the conversion table, thecircuitry: may select, as the conversion table, a first table from theplurality of tables when the preceding basic block is present at thesame frequency level and the number of non-zero coefficients included inthe preceding basic block is a first number; and may select, as theconversion table, a second table from the plurality of tables when thepreceding basic block is present at the same frequency level and thenumber of non-zero coefficients included in the preceding basic block isa second number larger than the first number, the second table having asmaller difference between a longest bit length and a shortest bitlength of a plurality of binary values than the first table.

In this way, when the number of non-zero coefficients of the currentbasic block is estimated to be large according to the number of non-zerocoefficients of the preceding basic block, the encoder is capable ofselecting the table in which the difference in bit length is small asthe conversion table, and assisting reduction in increase in codingamount.

In addition, for example, when selecting the conversion table, thecircuitry may select, from the plurality of tables, the conversion tablewhich has a smaller difference between a longest bit length and ashortest bit length of a plurality of binary values than a predetermineddifference, in the case where (i) a preceding basic block which is abasic block located before the current basic block in a predeterminedscan order defined in a descending order of frequencies of the one ormore basic blocks is not present at the same frequency level as afrequency level at the position of the current basic block and (ii) aspecific basic block which is a basic block including a non-zerocoefficient first in the predetermined scan order is present at afrequency level higher than the frequency level at the position of thecurrent basic block.

In this way, when the number of non-zero coefficients is estimated to belarge according to the relationship between the current basic block andthe specific basic block, the encoder is capable of selecting the tablein which the difference in bit length is small as the conversion table,and assisting reduction in increase in coding amount.

In addition, for example, when selecting the conversion table, thecircuitry may select the conversion table which has a smallestdifference between a longest bit length and a shortest bit length of aplurality of binary values from the plurality of tables when thepreceding basic block is not present at the same frequency level and thespecific basic block is present at the frequency level higher than thefrequency level at the position of the current basic block.

In this way, when the number of non-zero coefficients is estimated to belarge according to the relationship between the current basic block andthe specific basic block, the encoder is capable of selecting the tablein which the difference in bit length is small as the conversion table,and assisting reduction in increase in coding amount.

In addition, for example, when selecting the conversion table, thecircuitry may select the conversion table according to the number ofnon-zero coefficients estimated to be the number of non-zerocoefficients included in the current basic block based on a neighboringfrequency transform block which is a frequency transform block locatedaround the current frequency transform block, in the case where (i) apreceding basic block which is a basic block located before the currentbasic block in a predetermined scan order defined in a descending orderof frequencies of the one or more basic blocks is not present at thesame frequency level as a frequency level at the position of the currentbasic block and (ii) a specific basic block which is a basic blockincluding a non-zero coefficient first in the predetermined scan orderis not present at a frequency level higher than a frequency level at aposition of the current basic block.

In this way, the encoder is capable of selecting the conversion tableusing the neighboring frequency transform block which is estimated tohave a similar number of non-zero coefficients with respect to thenumber of non-zero coefficients of the current basic block.

In addition, for example, when selecting the conversion table, thecircuitry: may select a first table as the conversion table from theplurality of tables, when (i) the preceding basic block is not presentat the same frequency level, (ii) the specific basic block is notpresent at the higher frequency level, and (iii) the number of non-zerocoefficients estimated to be the number of non-zero coefficients basedon the neighboring frequency transform block is a first number; and mayselect a second table which has a smaller difference between a longestbit length and a shortest bit length of a plurality of binary valuesthan the first table as the conversion table from the plurality oftables, when (i) the preceding basic block is not present at the samefrequency level, (ii) the specific basic block is not present at thehigher frequency level, and (iii) the number of non-zero coefficientsestimated to be the number of non-zero coefficients based on theneighboring frequency transform block is a second number larger than thefirst number.

In this way, when the number of non-zero coefficients of the currentbasic block is estimated to be large according to the neighboringfrequency transform block, the encoder is capable of selecting the tablein which the difference in bit length is small as the conversion table,and assisting reduction in increase in coding amount.

In addition, for example, the neighboring frequency transform block maybe one of (i) a frequency transform block adjacent to a left of or abovethe current frequency transform block, (ii) a frequency transform blockwhich has been encoded immediately before the current frequencytransform block, and (iii) a frequency transform block which is locatedwithin a predetermined range from the current frequency transform blockand is the same as the current frequency transform block in coding mode,the coding mode being one of an inter prediction mode and an intraprediction mode.

In this way, the encoder is capable of selecting the conversion tableusing the appropriate neighboring frequency transform block.

In addition, for example, the number of non-zero coefficients estimatedbased on the neighboring frequency transform block may be estimatedbased on one of (i) the number of non-zero coefficients included in abasic block which is one of the one or more basic blocks in theneighboring frequency transform block and whose position relative to theneighboring frequency transform block is equivalent to a position of thecurrent basic block relative to the current frequency transform blockand (ii) the number of non-zero coefficients included in an entirety ofthe neighboring frequency transform block.

In this way, the encoder is capable of selecting the conversion tableaccording to the number of non-zero coefficients which is appropriatelyestimated based on the neighboring frequency transform block.

In addition, for example, when selecting the conversion table, thecircuitry may select the conversion table according to whether a codingmode of the current basic block is an inter prediction mode or an intraprediction mode, in the case where (i) a preceding basic block which isa basic block located before the current basic block in a predeterminedscan order defined in a descending order of frequencies of the one ormore basic blocks is not present at the same frequency level as afrequency level at the position of the current basic block and (ii) aspecific basic block which is a basic block including a non-zerocoefficient first in the predetermined scan order is not present at afrequency level higher than a frequency level at the position of thecurrent basic block.

In this way, the encoder is capable of selecting the conversion tableaccording to the coding mode which is the inter prediction mode or theintra prediction mode. The characteristics of the number of non-zerocoefficients are estimated to be different depending on the coding mode.Accordingly, the encoder is capable of reflecting the characteristic ofthe number of non-zero coefficients in the selection of the conversiontable, using the coding mode. Accordingly, the encoder is capable ofappropriately selecting the conversion table, and assisting reduction incoding amount of the frequency transform coefficient information.

In addition, for example, when selecting the conversion table, thecircuitry: may select, as the conversion table, a first table from theplurality of tables when (i) the preceding basic block is not present atthe same frequency level, (ii) the specific basic block is not presentat the higher level, and (iii) the coding mode of the current basicblock is an inter prediction mode; and may select, as the conversiontable, a second table from the plurality of tables when (i) thepreceding basic block is not present at the same frequency level, (ii)the specific basic block is not present at the higher level, and (iii)the coding mode for the current basic block is an intra prediction mode,the second table having a smaller difference between a longest bitlength and a shortest bit length of a plurality of binary values thanthe first table.

In this way, the encoder is capable of selecting the table having thesmall difference in bit length as the conversion table when the codingmode is the intra prediction mode in which a prediction accuracy is low,and the number of non-zero coefficients is large, thereby assistingreduction in increase in coding amount.

In addition, for example, when selecting the conversion table, thecircuitry may select the conversion table according to a quantizationparameter which is used to encode the current basic block, in the casewhere (i) a preceding basic block which is a basic block located beforethe current basic block in a predetermined scan order defined in adescending order of frequencies of the one or more basic blocks is notpresent at the same frequency level as a frequency level at the positionof the current basic block and (ii) a specific basic block which is abasic block including a non-zero coefficient first in the predeterminedscan order is not present at a frequency level higher than a frequencylevel at the position of the current basic block.

In this way, the encoder is capable of selecting the conversion tableaccording to the quantization parameter which is used to encode thecurrent basic block. The characteristics of the number of non-zerocoefficients are estimated to be different depending on the quantizationparameter. Accordingly, the encoder is capable of reflecting thecharacteristic of the number of non-zero coefficients in the selectionof the conversion table, using the quantization parameter. Accordingly,the encoder is capable of appropriately selecting the conversion table,and assisting reduction in coding amount of the frequency transformcoefficient information.

In addition, for example, when selecting the conversion table, thecircuitry: may select a first table as the conversion table from theplurality of tables, when (i) the preceding basic block is not presentat the same frequency level, (ii) the specific basic block is notpresent at the higher frequency level, and (iii) the quantizationparameter is a first value; and may select a second table which has asmaller difference than the first table as the conversion table from theplurality of tables, when (i) the preceding basic block is not presentat the same frequency level, (ii) the specific basic block is notpresent at the higher frequency level, and (iii) the quantizationparameter is a second value smaller than the first value, the secondtable having a smaller difference between a longest bit length and ashortest bit length of a plurality of binary values than the firsttable.

In this way, the encoder is capable of selecting the table having thesmall difference in bit length as the conversion table when thequantization parameter is small and thus the number of non-zerocoefficients is estimated to be large, thereby assisting reduction inincrease in coding amount.

In addition, for example, the circuitry: may encode the imageinformation, and may output a bitstream in which the image informationhas been encoded; when encoding the image information and outputting thebitstream: may binarize the image information; may switch whether or notto apply arithmetic encoding to a binary data string in which the imageinformation has been binarized; when arithmetic encoding is applied tothe binary data string, may apply arithmetic encoding to the binary datastring, and may output the bitstream which includes the binary datastring to which arithmetic encoding has been applied; and whenarithmetic encoding is not applied to the binary data string, may skipapplying arithmetic encoding to the binary data string and may outputthe bitstream which includes the binary data string to which arithmeticencoding has not been applied, and when binarizing the imageinformation, may binarize frequency transform coefficient informationwhich is related to frequency components of an image and included in theimage information, according to different binarization formats betweenwhen arithmetic encoding is applied to the binary data string and whenarithmetic encoding is not applied to the binary data string; whenbinarizing the image information, may binarize a part or an entirety ofprediction parameter information which is related to prediction methodsof an image and included in the image information, according to a commonbinarization format between when arithmetic encoding is applied to thebinary data string and when arithmetic encoding is not applied to thebinary data string; and when binarizing the frequency transformcoefficient information in the case where arithmetic encoding is notapplied to the binary data string, may binarize the data value includedin the frequency transform coefficient information, according to theconversion table selected from the plurality of tables based on theposition of the current basic block.

In this way, when arithmetic encoding is not applied, the encoder iscapable of assisting reduction in coding amount of frequency transformcoefficient information, using the conversion table selected from theplurality of tables according to the position of the current basicblock.

In addition, a decoder according to an aspect of the present disclosuremay be a decoder which decodes image information, the decoder including:memory; and circuitry accessible to the memory, wherein the circuitryaccessible to the memory: inverse binarizes a binary value which hasbeen obtained by binarizing a data value, according to a conversiontable in which a plurality of data values and a plurality of binaryvalues are associated with each other, to decode the image informationwhich includes the data value, the data value indicating the number ofnon-zero coefficients included in a current basic block which is one ofone or more basic blocks in a frequency transform block composed of aplurality of frequency transform coefficients; and when inversebinarizing the binary value, selects the conversion table from aplurality of tables including two or more tables which differ from eachother in difference between a longest bit length and a shortest bitlength of a plurality of binary values associated with the plurality ofdata values, according to a position of the current basic block in thecurrent frequency transform block which is the frequency transform blockincluding the current basic block, and inverse binarizes the binaryvalue according to the conversion table selected.

In this way, the decoder is capable of appropriately decoding theinformation for efficiently representing the plurality of frequencytransform coefficients which constitute the basic block. In this way,the decoder is capable of selecting the conversion table for inversebinarizing the data value indicating the number of non-zerocoefficients, according to the position of the current basic block. Thecharacteristics of the number of non-zero coefficients differ dependingon the position of the current basic block. Accordingly, the decoder iscapable of reflecting the characteristics of the number of non-zerocoefficients in the selection of the conversion table, using theposition of the current basic block. Accordingly, the decoder is capableof appropriately selecting the conversion table, and assisting reductionin coding amount of the frequency transform coefficient information.

For example, when selecting the conversion table, the circuitry mayselect the conversion table according to the number of non-zerocoefficients included in a preceding basic block which is a basic blocklocated before the current basic block in a predetermined scan orderdefined in a descending order of frequencies of the one or more basicblocks in the case where the preceding basic block is present at thesame frequency level as a frequency level at the position of the currentbasic block.

In this way, the decoder is capable of selecting the conversion tableaccording to the non-zero coefficients of the preceding basic blockwhich is estimated to have a similar number of non-zero coefficientswith respect to the number of non-zero coefficients of the current basicblock.

In addition, for example, when selecting the conversion table, thecircuitry: may select, as the conversion table, a first table from theplurality of tables when the preceding basic block is present at thesame frequency level and the number of non-zero coefficients included inthe preceding basic block is a first number; and may select, as theconversion table, a second table from the plurality of tables when thepreceding basic block is present at the same frequency level and thenumber of non-zero coefficients included in the preceding basic block isa second number larger than the first number, the second table having asmaller difference between a longest bit length and a shortest bitlength of a plurality of binary values than the first table.

In this way, when the number of non-zero coefficients of the currentbasic block is estimated to be large according to the number of non-zerocoefficients of the preceding basic block, the decoder is capable ofselecting the table in which the difference in bit length is small asthe conversion table, and assisting reduction in increase in codingamount.

In addition, for example, when selecting the conversion table, thecircuitry may select, from the plurality of tables, the conversion tablewhich has a smaller difference between a longest bit length and ashortest bit length of a plurality of binary values than a predetermineddifference, in the case where (i) a preceding basic block which is abasic block located before the current basic block in a predeterminedscan order defined in a descending order of frequencies of the one ormore basic blocks is not present at the same frequency level as afrequency level at the position of the current basic block and (ii) aspecific basic block which is a basic block including a non-zerocoefficient first in the predetermined scan order is present at afrequency level higher than the frequency level at the position of thecurrent basic block.

In this way, when the number of non-zero coefficients is estimated to belarge according to the relationship between the current basic block andthe specific basic block, the decoder is capable of selecting the tablein which the difference in bit length is small as the conversion table,and assisting reduction in increase in coding amount.

In addition, for example, when selecting the conversion table, thecircuitry may select the conversion table which has a smallestdifference between a longest bit length and a shortest bit length of aplurality of binary values from the plurality of tables when thepreceding basic block is not present at the same frequency level and thespecific basic block is present at the frequency level higher than thefrequency level at the position of the current basic block.

In this way, when the number of non-zero coefficients is estimated to belarge according to the relationship between the current basic block andthe specific basic block, the decoder is capable of selecting the tablein which the difference in bit length is small as the conversion table,and assisting reduction in increase in coding amount.

In addition, for example, when selecting the conversion table, thecircuitry may select the conversion table according to the number ofnon-zero coefficients estimated to be the number of non-zerocoefficients included in the current basic block based on a neighboringfrequency transform block which is a frequency transform block locatedaround the current frequency transform block, in the case where (i) apreceding basic block which is a basic block located before the currentbasic block in a predetermined scan order defined in a descending orderof frequencies of the one or more basic blocks is not present at thesame frequency level as a frequency level at the position of the currentbasic block and (ii) a specific basic block which is a basic blockincluding a non-zero coefficient first in the predetermined scan orderis not present at a frequency level higher than a frequency level at aposition of the current basic block.

In this way, the decoder is capable of selecting the conversion tableusing the neighboring frequency transform block which is estimated tohave a similar number of non-zero coefficients with respect to thenumber of non-zero coefficients of the current basic block.

In addition, for example, when selecting the conversion table, thecircuitry: may select a first table as the conversion table from theplurality of tables, when (i) the preceding basic block is not presentat the same frequency level, (ii) the specific basic block is notpresent at the higher frequency level, and (iii) the number of non-zerocoefficients estimated to be the number of non-zero coefficients basedon the neighboring frequency transform block is a first number; and mayselect a second table which has a smaller difference between a longestbit length and a shortest bit length of a plurality of binary valuesthan the first table as the conversion table from the plurality oftables, when (i) the preceding basic block is not present at the samefrequency level, (ii) the specific basic block is not present at thehigher frequency level, and (iii) the number of non-zero coefficientsestimated to be the number of non-zero coefficients based on theneighboring frequency transform block is a second number larger than thefirst number.

In this way, when the number of non-zero coefficients of the currentbasic block is estimated to be large according to the neighboringfrequency transform block, the decoder is capable of selecting the tablein which the difference in bit length is small as the conversion table,and assisting reduction in increase in coding amount.

In addition, for example, the neighboring frequency transform block maybe one of (i) a frequency transform block adjacent to a left of or abovethe current frequency transform block, (ii) a frequency transform blockwhich has been encoded immediately before the current frequencytransform block, and (iii) a frequency transform block which is locatedwithin a predetermined range from the current frequency transform blockand is the same as the current frequency transform block in coding mode,the coding mode being one of an inter prediction mode and an intraprediction mode.

In this way, the decoder is capable of selecting the conversion tableusing the appropriate neighboring frequency transform block.

In addition, for example, the number of non-zero coefficients estimatedbased on the neighboring frequency transform block may be estimatedbased on one of (i) the number of non-zero coefficients included in abasic block which is one of the one or more basic blocks in theneighboring frequency transform block and whose position relative to theneighboring frequency transform block is equivalent to a position of thecurrent basic block relative to the current frequency transform blockand (ii) the number of non-zero coefficients included in an entirety ofthe neighboring frequency transform block.

In this way, the decoder is capable of selecting the conversion tableaccording to the number of non-zero coefficients which is appropriatelyestimated based on the neighboring frequency transform block.

In addition, for example, when selecting the conversion table, thecircuitry may select the conversion table according to whether a codingmode of the current basic block is an inter prediction mode or an intraprediction mode, in the case where (i) a preceding basic block which isa basic block located before the current basic block in a predeterminedscan order defined in a descending order of frequencies of the one ormore basic blocks is not present at the same frequency level as afrequency level at the position of the current basic block and (ii) aspecific basic block which is a basic block including a non-zerocoefficient first in the predetermined scan order is not present at afrequency level higher than a frequency level at the position of thecurrent basic block.

In this way, the decoder is capable of selecting the conversion tableaccording to the coding mode which is the inter prediction mode or theintra prediction mode. The characteristics of the number of non-zerocoefficients are estimated to be different depending on the coding mode.Accordingly, the decoder is capable of reflecting the characteristics ofthe number of non-zero coefficients in the selection of the conversiontable, using the coding mode. Accordingly, the decoder is capable ofappropriately selecting the conversion table, and assisting reduction incoding amount of the frequency transform coefficient information.

In addition, for example, when selecting the conversion table, thecircuitry: may select, as the conversion table, a first table from theplurality of tables when (i) the preceding basic block is not present atthe same frequency level, (ii) the specific basic block is not presentat the higher level, and (iii) the coding mode of the current basicblock is an inter prediction mode; and may select, as the conversiontable, a second table from the plurality of tables when (i) thepreceding basic block is not present at the same frequency level, (ii)the specific basic block is not present at the higher level, and (iii)the coding mode for the current basic block is an intra prediction mode,the second table having a smaller difference between a longest bitlength and a shortest bit length of a plurality of binary values thanthe first table.

In this way, the decoder is capable of selecting the table having thesmall difference in bit length as the conversion table when the codingmode is the intra prediction mode in which the prediction accuracy islow and the number of non-zero coefficients is large, thereby assistingreduction in increase in coding amount.

In addition, for example, when selecting the conversion table, thecircuitry may select the conversion table according to a quantizationparameter which is used to encode the current basic block, in the casewhere (i) a preceding basic block which is a basic block located beforethe current basic block in a predetermined scan order defined in adescending order of frequencies of the one or more basic blocks is notpresent at the same frequency level as a frequency level at the positionof the current basic block and (ii) a specific basic block which is abasic block including a non-zero coefficient first in the predeterminedscan order is not present at a frequency level higher than a frequencylevel at the position of the current basic block.

In this way, the decoder is capable of selecting the conversion tableaccording to the quantization parameter which is used to decode thecurrent basic block. The characteristics of the number of non-zerocoefficients are estimated to be different depending on the quantizationparameter. Accordingly, the decoder is capable of reflecting thecharacteristic of the number of non-zero coefficients in the selectionof the conversion table, using the quantization parameter. Accordingly,the decoder is capable of appropriately selecting the conversion table,and assisting reduction in coding amount of the frequency transformcoefficient information.

In addition, for example, when selecting the conversion table, thecircuitry: may select a first table as the conversion table from theplurality of tables, when (i) the preceding basic block is not presentat the same frequency level, (ii) the specific basic block is notpresent at the higher frequency level, and (iii) the quantizationparameter is a first value; and may select a second table which has asmaller difference than the first table as the conversion table from theplurality of tables, when (i) the preceding basic block is not presentat the same frequency level, (ii) the specific basic block is notpresent at the higher frequency level, and (iii) the quantizationparameter is a second value smaller than the first value, the secondtable having a smaller difference between a longest bit length and ashortest bit length of a plurality of binary values than the firsttable.

In this way, the decoder is capable of selecting the table having thesmall difference in bit length as the conversion table when thequantization parameter is small and thus the number of non-zerocoefficients is estimated to be large, thereby assisting reduction inincrease in coding amount.

In addition, for example, the circuitry: may obtain a bitstream in whichthe image information has been encoded, and may decode the imageinformation; when obtaining the bitstream and decoding the imageinformation: may obtain the bitstream which includes a binary datastring in which the image information has been binarized; may switchwhether or not to apply arithmetic decoding to the binary data stringwhich is included in the bitstream; when arithmetic decoding is appliedto the binary data string, may apply arithmetic decoding to the binarydata string, and may inverse binarize the binary data string to whicharithmetic decoding has been applied, to decode the image information;and when arithmetic decoding is not applied to the binary data string,may skip applying arithmetic decoding to the binary data string, and mayinverse binarize the binary data string to which arithmetic decoding hasnot been applied, to decode the image information; when inversebinarizing the binary data string, may inverse binarize a first portionwhich is included in the binary data string and in which frequencytransform coefficient information related to frequency components of animage has been binarized, according to different inverse binarizationformats between when arithmetic decoding is applied to the binary datastring and when arithmetic decoding is not applied to the binary datastring; when inverse binarizing the binary data string, may inversebinarize a second portion which is included in the binary data stringand in which a part or an entirety of prediction parameter informationrelated to prediction methods of the image has been binarized, accordingto a common inverse binarization format between when arithmetic decodingis applied to the binary data string and when arithmetic decoding is notapplied to the binary data string; and when inverse binarizing the firstportion in the case where arithmetic decoding is not applied to thebinary data string, may inverse binarize the binary value included inthe first portion, according to the conversion table selected from theplurality of tables based on a position of the current basic block.

In this way, when arithmetic decoding is not applied, the decoder iscapable of assisting reduction in coding amount of frequency transformcoefficient information, using the conversion table which is selectedfrom the plurality of tables according to the position of the currentbasic block.

Furthermore, an encoding method according to an aspect of the presentdisclosure may be an encoding method for encoding image information, theencoding method including: binarizing a data value indicating the numberof non-zero coefficients included in a current basic block which is oneof one or more basic blocks in a frequency transform block composed of aplurality of frequency transform coefficients, according to a conversiontable in which a plurality of data values and a plurality of binaryvalues are associated with each other, to encode the image informationwhich includes the data value; and in the binarizing of the data value,selecting the conversion table from a plurality of tables including twoor more tables which differ from each other in difference between alongest bit length and a shortest bit length of a plurality of binaryvalues associated with the plurality of data values, according to aposition of the current basic block in the current frequency transformblock which is the frequency transform block including the current basicblock, and binarizing the data value according to the conversion tableselected.

In this way, the apparatus, etc. which performs the encoding method iscapable of appropriately encoding the information for efficientlyrepresenting the plurality of frequency transform coefficients whichconstitute the basic block. In this way, the apparatus, etc. whichperforms the encoding method is capable of selecting the conversiontable for binarizing the data value indicating the number of non-zerocoefficients, according to the position of the current basic block. Thecharacteristics of the number of non-zero coefficients differ dependingon the position of the current basic block. Accordingly, the apparatus,etc. which performs the encoding method is capable of reflecting thecharacteristics of the number of non-zero coefficients in the selectionof the conversion table, using the position of the current basic block.Accordingly, the apparatus, etc. which performs the encoding method iscapable of appropriately selecting the conversion table, and assistingreduction in coding amount of the frequency transform coefficientinformation.

Furthermore, a decoding method according to an aspect of the presentdisclosure may be a decoding method for decoding image information, thedecoding method including: inverse binarizing a binary value which hasbeen obtained by binarizing a data value, according to a conversiontable in which a plurality of data values and a plurality of binaryvalues are associated with each other, to decode the image informationwhich includes the data value, the data value indicating the number ofnon-zero coefficients included in a current basic block which is one ofone or more basic blocks in a frequency transform block composed of aplurality of frequency transform coefficients; and in the inversebinarizing of the binary value, selecting the conversion table from aplurality of tables including two or more tables which differ from eachother in difference between a longest bit length and a shortest bitlength of a plurality of binary values associated with the plurality ofdata values, according to a position of the current basic block in thecurrent frequency transform block which is the frequency transform blockincluding the current basic block, and inverse binarizing the binaryvalue according to the conversion table selected.

In this way, the apparatus, etc. which performs the decoding method iscapable of appropriately decoding the information for efficientlyrepresenting the plurality of frequency transform coefficients whichconstitute the basic block. In this way, the apparatus, etc. whichperforms the decoding method is capable of selecting the conversiontable for inverse binarizing the binary value of the data valueindicating the number of non-zero coefficients, according to theposition of the current basic block. The characteristics of the numberof non-zero coefficients differ depending on the position of the currentbasic block. Accordingly, the apparatus, etc. which performs thedecoding method is capable of reflecting the characteristics of thenumber of non-zero coefficients in the selection of the conversiontable, using the position of the current basic block. Accordingly, theapparatus, etc. which performs the decoding method is capable ofappropriately selecting the conversion table, and assisting reduction incoding amount of the frequency transform coefficient information.

Furthermore, these general and specific aspects may be implemented usinga system, an apparatus, a method, an integrated circuit, a computerprogram, or a computer-readable recording medium such as a CD-ROM, orany combination of systems, apparatuses, methods, integrated circuits,computer programs, or computer-readable recording media.

Hereinafter, embodiments will be described with reference to thedrawings.

It is to be noted that the embodiments described below each show ageneral or specific example. The numerical values, shapes, materials,constituent elements, the arrangement and connection of the constituentelements, steps, order of the steps, etc., indicated in the followingembodiments are mere examples, and therefore are not intended to limitthe scope of the claims. Therefore, among the constituent elements inthe following embodiments, those not recited in any of the independentclaims defining the most generic inventive concepts are described asoptional constituent elements.

Embodiment 1 [Encoder Outline]

First, the encoder according to Embodiment 1 will be outlined. FIG. 1 isa block diagram illustrating a functional configuration of encoder 100according to Embodiment 1. Encoder 100 is a moving picture/pictureencoder that encodes a moving picture/picture block by block.

As illustrated in FIG. 1, encoder 100 is a device that encodes a pictureblock by block, and includes splitter 102, subtractor 104, transformer106, quantizer 108, entropy encoder 110, inverse quantizer 112, inversetransformer 114, adder 116, block memory 118, loop filter 120, framememory 122, intra predictor 124, inter predictor 126, and predictioncontroller 128.

Encoder 100 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as splitter 102, subtractor104, transformer 106, quantizer 108, entropy encoder 110, inversequantizer 112, inverse transformer 114, adder 116, loop filter 120,intra predictor 124, inter predictor 126, and prediction controller 128.Alternatively, encoder 100 may be realized as one or more dedicatedelectronic circuits corresponding to splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, loop filter 120, intrapredictor 124, inter predictor 126, and prediction controller 128.

Hereinafter, each component included in encoder 100 will be described.

[Splitter]

Splitter 102 splits each picture included in an input moving pictureinto blocks, and outputs each block to subtractor 104. For example,splitter 102 first splits a picture into blocks of a fixed size (forexample, 128×128). The fixed size block is also referred to as codingtree unit (CTU). Splitter 102 then splits each fixed size block intoblocks of variable sizes (for example, 64×64 or smaller), based onrecursive quadtree and/or binary tree block splitting. The variable sizeblock is also referred to as a coding unit (CU), a prediction unit (PU),or a transform unit (TU). Note that in this embodiment, there is no needto differentiate between CU, PU, and TU; all or some of the blocks in apicture may be processed per CU, PU, or TU.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1. In FIG. 2, the solid lines represent block boundaries ofblocks split by quadtree block splitting, and the dashed lines representblock boundaries of blocks split by binary tree block splitting.

Here, block 10 is a square 128×128 pixel block (128×128 block). This128×128 block 10 is first split into four square 64×64 blocks (quadtreeblock splitting).

The top left 64×64 block is further vertically split into two rectangle32×64 blocks, and the left 32×64 block is further vertically split intotwo rectangle 16×64 blocks (binary tree block splitting). As a result,the top left 64×64 block is split into two 16×64 blocks 11 and 12 andone 32×64 block 13.

The top right 64×64 block is horizontally split into two rectangle 64×32blocks 14 and 15 (binary tree block splitting).

The bottom left 64×64 block is first split into four square 32×32 blocks(quadtree block splitting). The top left block and the bottom rightblock among the four 32×32 blocks are further split. The top left 32×32block is vertically split into two rectangle 16×32 blocks, and the right16×32 block is further horizontally split into two 16×16 blocks (binarytree block splitting). The bottom right 32×32 block is horizontallysplit into two 32×16 blocks (binary tree block splitting). As a result,the bottom left 64×64 block is split into 16×32 block 16, two 16×16blocks 17 and 18, two 32×32 blocks 19 and 20, and two 32×16 blocks 21and 22.

The bottom right 64×64 block 23 is not split.

As described above, in FIG. 2, block 10 is split into 13 variable sizeblocks 11 through 23 based on recursive quadtree and binary tree blocksplitting. This type of splitting is also referred to as quadtree plusbinary tree (QTBT) splitting.

Note that in FIG. 2, one block is split into four or two blocks(quadtree or binary tree block splitting), but splitting is not limitedto this example. For example, one block may be split into three blocks(ternary block splitting). Splitting including such ternary blocksplitting is also referred to as multi-type tree (MBT) splitting.

[Subtractor]

Subtractor 104 subtracts a prediction signal (prediction sample) from anoriginal signal (original sample) per block split by splitter 102. Inother words, subtractor 104 calculates prediction errors (also referredto as residuals) of a block to be encoded (hereinafter referred to as acurrent block). Subtractor 104 then outputs the calculated predictionerrors to transformer 106.

The original signal is a signal input into encoder 100, and is a signalrepresenting an image for each picture included in a moving picture (forexample, a luma signal and two chroma signals). Hereinafter, a signalrepresenting an image is also referred to as a sample.

[Transformer]

Transformer 106 transforms spatial domain prediction errors intofrequency domain transform coefficients, and outputs the transformcoefficients to quantizer 108. More specifically, transformer 106applies, for example, a predefined discrete cosine transform (DCT) ordiscrete sine transform (DST) to spatial domain prediction errors.

Note that transformer 106 may adaptively select a transform type fromamong a plurality of transform types, and transform prediction errorsinto transform coefficients by using a transform basis functioncorresponding to the selected transform type. This sort of transform isalso referred to as explicit multiple core transform (EMT) or adaptivemultiple transform (AMT).

The transform types include, for example, DCT-II, DCT-V DCT-VIII, DST-I,and DST-VII. FIG. 3 is a chart indicating transform basis functions foreach transform type. In FIG. 3, N indicates the number of input pixels.For example, selection of a transform type from among the plurality oftransform types may depend on the prediction type (intra prediction andinter prediction), and may depend on intra prediction mode.

Information indicating whether to apply such EMT or AMT (referred to as,for example, an AMT flag) and information indicating the selectedtransform type is signalled at the CU level. Note that the signaling ofsuch information need not be performed at the CU level, and may beperformed at another level (for example, at the sequence level, picturelevel, slice level, tile level, or CTU level).

Moreover, transformer 106 may apply a secondary transform to thetransform coefficients (transform result). Such a secondary transform isalso referred to as adaptive secondary transform (AST) or non-separablesecondary transform (NSST). For example, transformer 106 applies asecondary transform to each sub-block (for example, each 4×4 sub-block)included in the block of the transform coefficients corresponding to theintra prediction errors. Information indicating whether to apply NSSTand information related to the transform matrix used in NSST aresignalled at the CU level. Note that the signaling of such informationneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, or CTU level).

[Quantizer]

Quantizer 108 quantizes the transform coefficients output fromtransformer 106. More specifically, quantizer 108 scans, in apredetermined scanning order, the transform coefficients of the currentblock, and quantizes the scanned transform coefficients based onquantization parameters (QP) corresponding to the transformcoefficients. Quantizer 108 then outputs the quantized transformcoefficients (hereinafter referred to as quantized coefficients) of thecurrent block to entropy encoder 110 and inverse quantizer 112.

A predetermined order is an order for quantizing/inverse quantizingtransform coefficients. For example, a predetermined scanning order isdefined as ascending order of frequency (from low to high frequency) ordescending order of frequency (from high to low frequency).

A quantization parameter is a parameter defining a quantization stepsize (quantization width). For example, if the value of the quantizationparameter increases, the quantization step size also increases. In otherwords, if the value of the quantization parameter increases, thequantization error increases.

[Entropy Encoder]

Entropy encoder 110 generates an encoded signal (encoded bitstream) byvariable length encoding quantized coefficients, which are inputs fromquantizer 108. More specifically, entropy encoder 110, for example,binarizes quantized coefficients and arithmetic encodes the binarysignal.

[Inverse Quantizer]

Inverse quantizer 112 inverse quantizes quantized coefficients, whichare inputs from quantizer 108. More specifically, inverse quantizer 112inverse quantizes, in a predetermined scanning order, quantizedcoefficients of the current block. Inverse quantizer 112 then outputsthe inverse quantized transform coefficients of the current block toinverse transformer 114.

[Inverse Transformer]

Inverse transformer 114 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 112. More specifically, inverse transformer 114 restores theprediction errors of the current block by applying an inverse transformcorresponding to the transform applied by transformer 106 on thetransform coefficients. Inverse transformer 114 then outputs therestored prediction errors to adder 116.

Note that since information is lost in quantization, the restoredprediction errors do not match the prediction errors calculated bysubtractor 104. In other words, the restored prediction errors includequantization errors.

[Adder]

Adder 116 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 114, and prediction samples,which are inputs from prediction controller 128. Adder 116 then outputsthe reconstructed block to block memory 118 and loop filter 120. Areconstructed block is also referred to as a local decoded block.

[Block Memory] Block memory 118 is storage for storing blocks in apicture to be encoded (hereinafter referred to as a current picture) forreference in intra prediction. More specifically, block memory 118stores reconstructed blocks output from adder 116.[Loop Filter] Loop filter 120 applies a loop filter to blocksreconstructed by adder 116, and outputs the filtered reconstructedblocks to frame memory 122. A loop filter is a filter used in anencoding loop (in-loop filter), and includes, for example, a deblockingfilter (DF), a sample adaptive offset (SAO), and an adaptive loop filter(ALF).

In ALF, a least square error filter for removing compression artifactsis applied. For example, one filter from among a plurality of filters isselected for each 2×2 sub-block in the current block based on directionand activity of local gradients, and is applied.

More specifically, first, each sub-block (for example, each 2×2sub-block) is categorized into one out of a plurality of classes (forexample, 15 or 25 classes). The classification of the sub-block is basedon gradient directionality and activity. For example, classificationindex C is derived based on gradient directionality D (for example, 0 to2 or 0 to 4) and gradient activity A (for example, 0 to 4) (for example,C=5D+A). Then, based on classification index C, each sub-block iscategorized into one out of a plurality of classes (for example, 15 or25 classes).

For example, gradient directionality D is calculated by comparinggradients of a plurality of directions (for example, the horizontal,vertical, and two diagonal directions). Moreover, for example, gradientactivity A is calculated by summing gradients of a plurality ofdirections and quantizing the sum.

The filter to be used for each sub-block is determined from among theplurality of filters based on the result of such categorization.

The filter shape to be used in ALF is, for example, a circular symmetricfilter shape. FIG. 4A through FIG. 4C illustrate examples of filtershapes used in ALF. FIG. 4A illustrates a 5×5 diamond shape filter, FIG.4B illustrates a 7×7 diamond shape filter, and FIG. 4C illustrates a 9×9diamond shape filter. Information indicating the filter shape issignalled at the picture level. Note that the signaling of informationindicating the filter shape need not be performed at the picture level,and may be performed at another level (for example, at the sequencelevel, slice level, tile level, CTU level, or CU level). The enabling ordisabling of ALF is determined at the picture level or CU level. Forexample, for luma, the decision to apply ALF or not is done at the CUlevel, and for chroma, the decision to apply ALF or not is done at thepicture level. Information indicating whether ALF is enabled or disabledis signalled at the picture level or CU level. Note that the signalingof information indicating whether ALF is enabled or disabled need not beperformed at the picture level or CU level, and may be performed atanother level (for example, at the sequence level, slice level, tilelevel, or CTU

The coefficients set for the plurality of selectable filters (forexample, 15 or 25 filters) is signalled at the picture level. Note thatthe signaling of the coefficients set need not be performed at thepicture level, and may be performed at another level (for example, atthe sequence level, slice level, tile level, CTU level, CU level, orsub-block level).

[Frame Memory]

Frame memory 122 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 122 stores reconstructed blocks filtered byloop filter 120.

[Intra Predictor]

Intra predictor 124 generates a prediction signal (intra predictionsignal) by intra predicting the current block with reference to a blockor blocks in the current picture and stored in block memory 118 (alsoreferred to as intra frame prediction). More specifically, intrapredictor 124 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 128.

For example, intra predictor 124 performs intra prediction by using onemode from among a plurality of predefined intra prediction modes. Theintra prediction modes include one or more non-directional predictionmodes and a plurality of directional prediction modes.

The one or more non-directional prediction modes include, for example,planar prediction mode and DC prediction mode defined in theH.265/high-efficiency video coding (HEVC) standard (see NPTL 1).

The plurality of directional prediction modes include, for example, the33 directional prediction modes defined in the H.265/HEVC standard. Notethat the plurality of directional prediction modes may further include32 directional prediction modes in addition to the 33 directionalprediction modes (for a total of 65 directional prediction modes). FIG.5 illustrates 67 intra prediction modes used in intra prediction (twonon-directional prediction modes and 65 directional prediction modes).The solid arrows represent the 33 directions defined in the H.265/HEVCstandard, and the dashed arrows represent the additional 32 directions.

Note that a luma block may be referenced in chroma block intraprediction. In other words, a chroma component of the current block maybe predicted based on a luma component of the current block. Such intraprediction is also referred to as cross-component linear model (CCLM)prediction. Such a chroma block intra prediction mode that references aluma block (referred to as, for example, CCLM mode) may be added as oneof the chroma block intra prediction modes.

Intra predictor 124 may correct post-intra-prediction pixel values basedon horizontal/vertical reference pixel gradients. Intra predictionaccompanied by this sort of correcting is also referred to as positiondependent intra prediction combination (PDPC). Information indicatingwhether to apply PDPC or not (referred to as, for example, a PDPC flag)is, for example, signalled at the CU level. Note that the signaling ofthis information need not be performed at the CU level, and may beperformed at another level (for example, on the sequence level, picturelevel, slice level, tile level, or CTU level).

[Inter Predictor]

Inter predictor 126 generates a prediction signal (inter predictionsignal) by inter predicting the current block with reference to a blockor blocks in a reference picture, which is different from the currentpicture and is stored in frame memory 122 (also referred to as interframe prediction). Inter prediction is performed per current block orper sub-block (for example, per 4×4 block) in the current block. Forexample, inter predictor 126 performs motion estimation in a referencepicture for the current block or sub-block. Inter predictor 126 thengenerates an inter prediction signal of the current block or sub-blockby motion compensation by using motion information (for example, amotion vector) obtained from motion estimation. Inter predictor 126 thenoutputs the generated inter prediction signal to prediction controller128.

The motion information used in motion compensation is signalled. Amotion vector predictor may be used for the signaling of the motionvector. In other words, the difference between the motion vector and themotion vector predictor may be signalled.

Note that the inter prediction signal may be generated using motioninformation for a neighboring block in addition to motion informationfor the current block obtained from motion estimation. Morespecifically, the inter prediction signal may be generated per sub-blockin the current block by calculating a weighted sum of a predictionsignal based on motion information obtained from motion estimation and aprediction signal based on motion information for a neighboring block.Such inter prediction (motion compensation) is also referred to asoverlapped block motion compensation (OBMC).

In such an OBMC mode, information indicating sub-block size for OBMC(referred to as, for example, OBMC block size) is signalled at thesequence level. Moreover, information indicating whether to apply theOBMC mode or not (referred to as, for example, an OBMC flag) issignalled at the CU level. Note that the signaling of such informationneed not be performed at the sequence level and CU level, and may beperformed at another level (for example, at the picture level, slicelevel, tile level, CTU level, or sub-block level).

Note that the motion information may be derived on the decoder sidewithout being signalled. For example, a merge mode defined in theH.265/HEVC standard may be used. Moreover, for example, the motioninformation may be derived by performing motion estimation on thedecoder side. In this case, motion estimation is performed without usingthe pixel values of the current block.

Here, a mode for performing motion estimation on the decoder side willbe described. A mode for performing motion estimation on the decoderside is also referred to as pattern matched motion vector derivation(PMMVD) mode or frame rate up-conversion (FRUC) mode.

First, a candidate list (a candidate list may be a merge list) ofcandidates each including a motion vector predictor is generated withreference to motion vectors of encoded blocks that spatially ortemporally neighbor the current block. For example, evaluation valuesfor the candidates included in the candidate list are calculated and onecandidate is selected based on the calculated evaluation values.

Next, a motion vector for the current block is derived from the motionvector of the selected candidate. More specifically, for example, themotion vector for the current block is calculated as the motion vectorof the selected candidate, as-is. Alternatively, the motion vector forthe current block may be derived by pattern matching performed in thevicinity of a position in a reference picture corresponding to themotion vector of the selected candidate.

Note that an evaluation value is calculated by pattern matchingperformed between a region in a reference picture corresponding to amotion vector and a predetermined region.

The pattern matching used is either first pattern matching or secondpattern matching. First pattern matching and second pattern matching arealso referred to as bilateral matching and template matching,respectively.

In the first pattern matching, pattern matching is performed between twoblocks along the motion trajectory of the current block in two differentreference pictures. Therefore, in the first pattern matching, a regionin another reference picture conforming to the motion trajectory of thecurrent block is used as the predetermined region for theabove-described calculation of the candidate evaluation value.

FIG. 6 is for illustrating pattern matching (bilateral matching) betweentwo blocks along a motion trajectory. As illustrated in FIG. 6, in thefirst pattern matching, two motion vectors (MV0, MV1) are derived byfinding the best match between two blocks along the motion trajectory ofthe current block (Cur block) in two different reference pictures (Ref0,Ref1).

Under the assumption of continuous motion trajectory, the motion vectors(MV0, MV1) pointing to the two reference blocks shall be proportional tothe temporal distances (TD0, TD1) between the current picture (Cur Pic)and the two reference pictures (Ref0, Ref1.). For example, when thecurrent picture is temporally between the two reference pictures and thetemporal distance from the current picture to the two reference picturesis the same, the first pattern matching derives a mirror basedbi-directional motion vector.

In the second pattern matching, pattern matching is performed between atemplate in the current picture (blocks neighboring the current block inthe current picture (for example, the top and/or left neighboringblocks)) and a block in a reference picture. Therefore, in the secondpattern matching, a block neighboring the current block in the currentpicture is used as the predetermined region for the above-describedcalculation of the candidate evaluation value.

FIG. 7 is for illustrating pattern matching (template matching) betweena template in the current picture and a block in a reference picture. Asillustrated in FIG. 7, in the second pattern matching, a motion vectorof the current block is derived by searching a reference picture (Ref0)to find the block that best matches neighboring blocks of the currentblock (Cur block) in the current picture (Cur Pic).

Information indicating whether to apply the FRUC mode or not (referredto as, for example, a FRUC flag) is signalled at the CU level. Moreover,when the FRUC mode is applied (for example, when the FRUC flag is set totrue), information indicating the pattern matching method (first patternmatching or second pattern matching) is signalled at the CU level. Notethat the signaling of such information need not be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, CTU level, orsub-block level).

It is to be noted that motion information may be derived on the decoderside using a method different from motion estimation. For example, theamount of correction for a motion vector may be calculated using thepixel value of a neighboring pixel in units of a pixel, based on a modelassuming uniform linear motion.

Here, a mode for deriving a motion vector based on a model assuminguniform linear motion will be described. This mode is also referred toas a bi-directional optical flow (BIO) mode.

FIG. 8 is for illustrating a model assuming uniform linear motion. InFIG. 8, (v_(x), v_(y)) denotes a velocity vector, and τ₀ and τ₁ denotetemporal distances between the current picture (Cur Pic) and tworeference pictures (Ref₀, Ref₁). (MVx₀, MVy₀) denotes a motion vectorcorresponding to reference picture Ref₀, and (MVx₁, MVy₁) denotes amotion vector corresponding to reference picture Ref₁.

Here, under the assumption of uniform linear motion exhibited byvelocity vector (v_(x), v_(y)), (MVx₀, MVy₀) and (MVx₁, MVy₁) arerepresented as (v_(x)τ₀, v_(y)τ₀) and (−v_(x)τ₁, −v_(y)τ₁),respectively, and the following optical flow equation is given.

MATH. 1

∂I ^((k)) /∂t+v _(x) ∂I ^((k)) /∂x+v _(y) ∂I ^((k)) /∂y=0.  (1)

Here, I^((k)) denotes a luma value from reference picture k (k=0, 1)after motion compensation. This optical flow equation shows that the sumof (i) the time derivative of the luma value, (ii) the product of thehorizontal velocity and the horizontal component of the spatial gradientof a reference picture, and (iii) the product of the vertical velocityand the vertical component of the spatial gradient of a referencepicture is equal to zero. A motion vector of each block obtained from,for example, a merge list is corrected pixel by pixel based on acombination of the optical flow equation and Hermite interpolation.

Note that a motion vector may be derived on the decoder side using amethod other than deriving a motion vector based on a model assuminguniform linear motion. For example, a motion vector may be derived foreach sub-block based on motion vectors of neighboring blocks.

Here, a mode in which a motion vector is derived for each sub-blockbased on motion vectors of neighboring blocks will be described. Thismode is also referred to as affine motion compensation prediction mode.

FIG. 9 is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks. In FIG. 9, the currentblock includes 16 4×4 sub-blocks. Here, motion vector v₀ of the top leftcorner control point in the current block is derived based on motionvectors of neighboring sub-blocks, and motion vector v₁ of the top rightcorner control point in the current block is derived based on motionvectors of neighboring blocks. Then, using the two motion vectors v₀ andv₁, the motion vector (v_(x), v_(y)) of each sub-block in the currentblock is derived using Equation 2 below.

MATH.  2 $\begin{matrix}\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0y}}}\end{matrix} \right. & (2)\end{matrix}$

Here, x and y are the horizontal and vertical positions of thesub-block, respectively, and w is a predetermined weighted coefficient.

Such an affine motion compensation prediction mode may include a numberof modes of different methods of deriving the motion vectors of the topleft and top right corner control points. Information indicating such anaffine motion compensation prediction mode (referred to as, for example,an affine flag) is signalled at the CU level. Note that the signaling ofinformation indicating the affine motion compensation prediction modeneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, CTU level, or sub-block level).

[Prediction Controller]

Prediction controller 128 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto subtractor 104 and adder 116.

[Decoder Outline]

Next, a decoder capable of decoding an encoded signal (encodedbitstream) output from encoder 100 will be described. FIG. 10 is a blockdiagram illustrating a functional configuration of decoder 200 accordingto Embodiment 1. Decoder 200 is a moving picture/picture decoder thatdecodes a moving picture/picture block by block.

As illustrated in FIG. 10, decoder 200 includes entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, block memory210, loop filter 212, frame memory 214, intra predictor 216, interpredictor 218, and prediction controller 220.

Decoder 200 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, loop filter212, intra predictor 216, inter predictor 218, and prediction controller220. Alternatively, decoder 200 may be realized as one or more dedicatedelectronic circuits corresponding to entropy decoder 202, inversequantizer 204, inverse transformer 206, adder 208, loop filter 212,intra predictor 216, inter predictor 218, and prediction controller 220.

Hereinafter, each component included in decoder 200 will be described.

[Entropy Decoder]

Entropy decoder 202 entropy decodes an encoded bitstream. Morespecifically, for example, entropy decoder 202 arithmetic decodes anencoded bitstream into a binary signal. Entropy decoder 202 thendebinarizes the binary signal. With this, entropy decoder 202 outputsquantized coefficients of each block to inverse quantizer 204.

[Inverse Quantizer]

Inverse quantizer 204 inverse quantizes quantized coefficients of ablock to be decoded (hereinafter referred to as a current block), whichare inputs from entropy decoder 202. More specifically, inversequantizer 204 inverse quantizes quantized coefficients of the currentblock based on quantization parameters corresponding to the quantizedcoefficients. Inverse quantizer 204 then outputs the inverse quantizedcoefficients (i.e., transform coefficients) of the current block toinverse transformer 206.

[Inverse Transformer]

Inverse transformer 206 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 204.

For example, when information parsed from an encoded bitstream indicatesapplication of EMT or AMT (for example, when the AMT flag is set totrue), inverse transformer 206 inverse transforms the transformcoefficients of the current block based on information indicating theparsed transform type.

Moreover, for example, when information parsed from an encoded bitstreamindicates application of NSST, inverse transformer 206 applies asecondary inverse transform to the transform coefficients.

[Adder]

Adder 208 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 206, and prediction samples,which is an input from prediction controller 220. Adder 208 then outputsthe reconstructed block to block memory 210 and loop filter 212.

[Block Memory]

Block memory 210 is storage for storing blocks in a picture to bedecoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 210 storesreconstructed blocks output from adder 208.

[Loop Filter]

Loop filter 212 applies a loop filter to blocks reconstructed by adder208, and outputs the filtered reconstructed blocks to frame memory 214and, for example, a display device.

When information indicating the enabling or disabling of ALF parsed froman encoded bitstream indicates enabled, one filter from among aplurality of filters is selected based on direction and activity oflocal gradients, and the selected filter is applied to the reconstructedblock.

[Frame Memory]

Frame memory 214 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 214 stores reconstructed blocks filtered byloop filter 212.

[Intra Predictor]

Intra predictor 216 generates a prediction signal (intra predictionsignal) by intra prediction with reference to a block or blocks in thecurrent picture and stored in block memory 210. More specifically, intrapredictor 216 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 220.

Note that when an intra prediction mode in which a chroma block is intrapredicted from a luma block is selected, intra predictor 216 may predictthe chroma component of the current block based on the luma component ofthe current block.

Moreover, when information indicating the application of PDPC is parsedfrom an encoded bitstream, intra predictor 216 correctspost-intra-prediction pixel values based on horizontal/verticalreference pixel gradients.

[Inter Predictor]

Inter predictor 218 predicts the current block with reference to areference picture stored in frame memory 214. Inter prediction isperformed per current block or per sub-block (for example, per 4×4block) in the current block. For example, inter predictor 218 generatesan inter prediction signal of the current block or sub-block by motioncompensation by using motion information (for example, a motion vector)parsed from an encoded bitstream, and outputs the inter predictionsignal to prediction controller 220.

Note that when the information parsed from the encoded bitstreamindicates application of OBMC mode, inter predictor 218 generates theinter prediction signal using motion information for a neighboring blockin addition to motion information for the current block obtained frommotion estimation.

Moreover, when the information parsed from the encoded bitstreamindicates application of FRUC mode, inter predictor 218 derives motioninformation by performing motion estimation in accordance with thepattern matching method (bilateral matching or template matching) parsedfrom the encoded bitstream. Inter predictor 218 then performs motioncompensation using the derived motion information.

Moreover, when BIO mode is to be applied, inter predictor 218 derives amotion vector based on a model assuming uniform linear motion. Moreover,when the information parsed from the encoded bitstream indicates thataffine motion compensation prediction mode is to be applied, interpredictor 218 derives a motion vector of each sub-block based on motionvectors of neighboring blocks.

[Prediction Controller]

Prediction controller 220 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto adder 208.

[A Specific Configuration of the Entropy Encoder in the Encoder]

FIG. 11 is a block diagram illustrating a specific functionalconfiguration of entropy encoder 110 in encoder 100 according toEmbodiment 1. Entropy encoder 110 variable-length encodes quantizedcoefficients output from quantizer 108 to generate a bitstream, andoutputs the generated bitstream. The bitstream corresponds to encodedimage information, and is also referred to as an encoded signal, anencoded bitstream, or an encoded bit string.

In the example of FIG. 11, entropy encoder 110 includes: binarizer 132;switch 134; intermediate buffer 136; arithmetic encoder 138; switch 140;and multiplexer 142. Entropy encoder 110 generates a bitstream andoutputs the generated bitstream to store the generated bitstream inoutput buffer 144. The bitstream stored in output buffer 144 isarbitrarily output from output buffer 144. Entropy encoder 110 mayinclude output buffer 144.

[The Binarizer in the Entropy Encoder]

Binarizer 132 binarizes quantized coefficients, etc. More specifically,binarizer 132 converts quantized frequency transform coefficients, etc.into a data string in which each of the values is represented by 0 or 1,and outputs the resulting data string. Hereinafter, the data string isalso referred to as a binary data string. In addition, the binarizationperformed by binarizer 132 is basically binarization for arithmeticencoding, and more specifically for binary arithmetic encoding. In otherwords, binarizer 132 basically derives the binary data string of theimage information according to the binarization for arithmetic encoding.

It is to be noted that examples of binarization methods include: unarybinarization; truncated unary binarization; unary and kth orderexponential Golomb combined binarization; fixed length binarization,table reference, etc.

In addition, for example, entropy encoding according to a context-basedadaptive binary arithmetic coding method is performed as thebinarization by binarizer 132 and the arithmetic encoding by arithmeticencoder 138. The context-based adaptive binary arithmetic coding methodis also referred to as CABAC. The binarization performed by binarizer132 can be represented as binarization for context-based adaptive binaryarithmetic coding method.

[The Switch in the Entropy Encoder]

Switches 134 and 140 operate together according to mode information, andswitch whether or not to apply arithmetic encoding to the binary datastring. For example, switches 134 and 140 switch whether or not to applyarithmetic encoding to the binary data string according to modeinformation which is given from outside encoder 100. The modeinformation may be given as an instruction from a user, a host system,or the like.

For example, the mode information selectively indicates a first mode anda second mode. In other words, the mode information indicates a selectedone of the first mode and the second mode. For example, arithmeticencoding is applied to a binary data string in the first mode, andarithmetic encoding is not applied to a binary data string in the secondmode.

More specifically, when the mode information indicates the first mode,switch 134 outputs the binary data string output from binarizer 132 tointermediate buffer 136 so as to store the binary data string inintermediate buffer 136. Arithmetic encoder 138 applies arithmeticencoding to the binary data string stored in intermediate buffer 136,and outputs the binary data string to which arithmetic encoding has beenapplied. Switch 140 outputs the binary data string output fromarithmetic encoder 138 to multiplexer 142.

When the mode information indicates the second mode, switch 134 outputsthe binary data string output from binarizer 132 to switch 140 as it is.Switch 140 outputs the binary data string output from switch 134 tomultiplexer 142. In other words, arithmetic encoding is bypassed. It isto be noted that bypassing arithmetic encoding may be represented asskipping arithmetic encoding in order to avoid confusion with bypassarithmetic encoding which is an aspect of arithmetic encoding.

Mode information and a mode may be also represented as delay modeinformation and a delay mode, respectively. More specifically, the firstmode is a normal mode, and the second mode is a low delay mode.Processing delay is reduced more significantly in the second mode thanin the first mode.

[The Intermediate Buffer in the Entropy Encoder]

Intermediate buffer 136 is storage for storing binary data strings, andis also referred to as intermediate memory. Delay occurs in thearithmetic encoding performed by arithmetic encoder 138. In addition,the delay amount varies depending on the content of a binary datastring. Intermediate buffer 136 absorbs variation in delay amount, whichfacilitates the subsequent processing. It is to be noted that inputtingdata in the storage such as intermediate buffer 136, or the likecorresponds to storing data in the storage, and outputting the data fromthe storage corresponds to reading the data from the storage.

[The Arithmetic Encoder in the Entropy Encoder]

Arithmetic encoder 138 performs arithmetic encoding. More specifically,arithmetic encoder 138 reads the binary data string stored inintermediate buffer 136, and applies arithmetic encoding to the binarydata string. Arithmetic encoder 138 may apply arithmetic encoding to thebinary data string according to the context-based adaptive binary codingmethod.

For example, arithmetic encoder 138 selects an occurrence probabilityaccording to context of a data type, or the like, performs arithmeticencoding according to the selected occurrence probability, and updatesthe occurrence probability according to the result of the arithmeticencoding. In other words, arithmetic encoder 138 may perform arithmeticencoding according to the variable occurrence probability. Thearithmetic encoding performed according to the variable occurrenceprobability may be also referred to as context-based adaptive arithmeticcoding.

In addition, arithmetic encoder 138 may arithmetic encode data having aparticular data type, or the like according to a fixed occurrenceprobability. More specifically, arithmetic encoder 138 may performarithmetic encoding according to an occurrence probability of 50% as anoccurrence probability of 0 or 1. The arithmetic encoding performedaccording to the fixed occurrence probability may be also referred to asbypass arithmetic encoding.

[The Multiplexer in the Entropy Encoder]

Multiplexer 142 multiplexes mode information and a binary data string togenerate a bitstream including the mode information and the binary datastring. Multiplexer 142 outputs the bitstream to output buffer 144 so asto store the bitstream in output buffer 144. The bitstream stored inoutput buffer 144 is arbitrarily output from output buffer 144. In otherwords, multiplexer 142 outputs the bitstream via output buffer 144.

For example, the mode information may be included in the bitstream as ahigher-order parameter. More specifically, the mode information may beincluded in a sequence parameter set (SPS) in a bitstream, in a pictureparameter set (PPS) in the bitstream, or in the slice header in thebitstream. The mode information included in the bitstream is representedas one or more bits.

The binary data string may be included in the slice data. Here, thebinary data string may be a binary data string to which arithmeticencoding has been applied, or may be a binary data string to whicharithmetic encoding has not been applied.

In addition, the mode information included in the bitstream may berepresented also as application information indicating whether or notthe binary data string included in the bitstream has been arithmeticencoded. In other words, the mode information may be included in thebitstream as application information indicating whether or not thebinary data string included in the bitstream has been arithmeticencoded. The application information may indicate whether the bitstreamincludes the binary data string to which arithmetic encoding has beenapplied or the binary data string to which arithmetic encoding has notbeen applied.

It is to be noted that the mode information may not be included in thebitstream, for example, when the mode information is exchanged in thehost system and when the mode information is predefined. In other words,in this case, multiplexing does not need to be performed.

[The Output Buffer]

Output buffer 144 is storage for storing bitstreams, and is alsoreferred to as a coded picture buffer (CPB) or output memory. Abitstream which is obtained by means of encoder 100 encoding imageinformation is stored in output buffer 144. The bitstream stored inoutput buffer 144 is arbitrarily output, and is multiplexed with, forexample, an encoded audio signal, etc.

[A Specific Configuration of an Entropy Decoder in a Decoder]

FIG. 12 is a block diagram illustrating a specific functionalconfiguration of entropy decoder 202 in decoder 200 according toEmbodiment 1. Entropy decoder 202 derives quantized coefficients, etc.by entropy decoding a bitstream input via input buffer 232. Thebitstream is a bitstream generated by encoder 100 and has, for example,the above-described data structure.

In the example of FIG. 12, entropy decoder 202 includes: demultiplexer234; switch 236; arithmetic decoder 238; intermediate buffer 240; switch242; and inverse binarizer 244. Entropy decoder 202 may include inputbuffer 232.

[The Input Buffer]

Input buffer 232 is storage for storing bitstreams and is also referredto as a CPB or input memory. A bitstream decoded by decoder 200 is, forexample, demultiplexed from an encoded audio signal, etc. and is storedin input buffer 232. Decoder 200 reads the bitstream stored in inputbuffer 232, and decodes the bitstream.

[The Demultiplexer in the Entropy Decoder]

Demultiplexer 234 obtains a bitstream from input buffer 232,demultiplexes mode information and the binary data string from thebitstream, and outputs the mode information and the binary data string.In other words, demultiplexer 234 obtains the bitstream including themode information and the binary data string via input buffer 232, andoutputs the mode information and the binary data string included in thebitstream. The binary data string may be a binary data string to whicharithmetic encoding has been applied, or may be a binary data string towhich arithmetic encoding has not been applied.

As described above, the mode information may be represented also asapplication information indicating whether or not the binary data stringincluded in the bitstream to which arithmetic encoding has been applied.It is to be noted that the mode information may not be included in thebitstream, for example, when the mode information is exchanged in thehost system and when the mode information is predefined. In this case,the mode information does not need to be demultiplexed and output. Themode information may be given as an instruction from outside decoder200, specifically, from a user, the host system, or the like.

[The Switch in the Entropy Decoder]

Switches 236 and 242 operate together according to mode informationwhich is obtained from demultiplexer 234, or the like, and switcheswhether or not to apply arithmetic decoding to the binary data string.For example, arithmetic decoding is applied to the binary data string inthe first mode out of the first mode and the second mode selectivelyindicated by the mode information, and arithmetic decoding is notapplied to the binary data string in the second mode.

More specifically, when the mode information indicates the first mode,switch 236 outputs the binary data string which is output fromdemultiplexer 234 to arithmetic decoder 238. Arithmetic decoder 238applies arithmetic decoding to the binary data string, and outputs thebinary data string which has been arithmetic decoded to store the binarydata string to which arithmetic decoding has been applied inintermediate buffer 240. Switch 242 arbitrarily obtains the binary datastring stored in intermediate buffer 240, and outputs the binary datastring obtained from intermediate buffer 240 to inverse binarizer 244.

When the mode information indicates the second mode, switch 236 outputsthe binary data string which is output from demultiplexer 234 to switch242 as it is. Switch 242 outputs the binary data string output fromswitch 236 to inverse multiplexer 244. In other words, arithmeticdecoding is bypassed. It is to be noted that bypassing arithmeticdecoding may be represented as skipping arithmetic decoding in order toavoid confusion with bypass arithmetic decoding which is an aspect ofarithmetic decoding.

[The Arithmetic Decoder in the Entropy Decoder]

Arithmetic decoder 238 performs arithmetic decoding. Specifically,arithmetic decoder 238 applies arithmetic decoding to binary data stringto which arithmetic encoding has been applied, and outputs the binarydata string to which arithmetic decoding has been applied to store thebinary data string to which arithmetic decoding has been applied inintermediate buffer 240. The arithmetic decoded binary data stringcorresponds to the original binary data string to which arithmeticencoding has not been applied. Arithmetic decoder 238 may applyarithmetic decoding to the binary data string according to thecontext-based adaptive binary coding method.

For example, arithmetic decoder 238 selects an occurrence probabilityaccording to context of a data type, or the like, performs arithmeticdecoding according to the selected occurrence probability, and updatesthe occurrence probability according to the result of the arithmeticdecoding. In other words, arithmetic decoder 238 may perform arithmeticdecoding according to the variable occurrence probability. Thearithmetic decoding performed according to the variable occurrenceprobability may be also referred to as context-based adaptive arithmeticdecoding.

In addition, arithmetic decoder 238 may arithmetic decode data having aparticular data type, or the like according to a fixed occurrenceprobability. Specifically, arithmetic decoder 238 may perform arithmeticdecoding according to an occurrence probability of 50% as an occurrenceprobability of 0 or 1. The arithmetic decoding performed according to afixed occurrence probability is also referred to as bypass arithmeticdecoding.

[The Intermediate Buffer in the Entropy Decoder]

Intermediate buffer 240 is storage for storing binary data strings whichhave been arithmetic decoded, and is also referred to as intermediatememory. Delay occurs in the arithmetic decoding performed by arithmeticdecoder 238. In addition, the delay amount varies depending on thecontent of a binary data string. Intermediate buffer 240 absorbsvariation in delay amount, which facilitates the subsequent processing.

[The Inverse Binarizer in the Entropy Decoder]

Inverse binarizer 244 derives quantized coefficients, etc. by inversebinarizing a binary data string. Specifically, inverse binarizer 244converts the binary data string in which each of values is representedas 0 or 1 into quantized frequency transform coefficients, etc., andoutputs the quantized frequency transform coefficients, etc. to inversequantizer 204. In addition, inverse binarization performed by inversebinarizer 244 is basically inverse binarization corresponding tobinarization for arithmetic encoding, and more specifically inversebinarization corresponding to binarization for binary arithmeticencoding.

In addition, for example, entropy decoding according to a context-basedadaptive binary arithmetic coding method is performed as the arithmeticdecoding by arithmetic decoder 238 and the inverse binarization byinverse binarizer 244. In other words, inverse binarizer 244 may performinverse binarization corresponding to the context-based binaryarithmetic coding method. In addition, the inverse binarization is alsoreferred to as multi-value processing.

[To Apply or Skip Applying Arithmetic Encoding and Arithmetic Decoding]

Encoder 100 and decoder 200 according to this embodiment areparticularly applicable to real-time communication systems, etc. inwhich encoding and decoding are desired to be performed in a short time.Specifically, encoder 100 and decoder 200 are applicable toteleconference systems, electronic mirrors, etc. For example, in thesesystem environments, a second mode in which arithmetic encoding andarithmetic decoding are not performed is used.

In addition, application information basically indicates, in units of atleast one entire picture, whether arithmetic encoding has been appliedto a binary data string included in a bitstream. In addition, whether ornot to apply arithmetic encoding is switched in units of at least oneentire picture.

However, whether or not to apply arithmetic encoding may be switched insmaller unit. For example, arithmetic encoding and arithmetic decodingmay be skipped for data having a particular data type. Morespecifically, arithmetic encoding and arithmetic decoding may be skippedinstead of bypass arithmetic encoding and bypass arithmetic decoding.

In addition, for example, switching between context arithmetic encoding,bypass arithmetic encoding, and arithmetic encoding may be performed.Likewise, switching between context arithmetic decoding, bypassarithmetic decoding, and arithmetic decoding may be performed.

In addition, application information indicating whether or notarithmetic encoding has been applied to a binary data string may berepresented by a 1-bit flag or in another form. For example, by adding,to a bitstream, information indicating that arithmetic encoding has beenapplied to a binary data string, the bitstream can include additionalinformation as application information. Alternatively, by adding, to abitstream, information indicating that arithmetic encoding has beenapplied to a binary data string, the bitstream can include additionalinformation as application information.

In addition, the application information may be included in thebitstream as information common to the other information. For example,when information indicating the type of a picture has been included inthe bitstream and whether or not to apply arithmetic encoding isswitched according to the type of the picture, the informationindicating the type of the picture may be application information.

[Switching Syntax Structures]

Coding amounts may vary significantly depending on whether arithmeticencoding and arithmetic decoding are applied. In particular, theinformation amount of frequency transform coefficient informationrelated to frequency components of an image is large. Accordingly, whenarithmetic encoding and arithmetic decoding are not used for suchfrequency transform coefficient information, the coding amount may beextremely large.

In view of this, binarizer 132 of encoder 100 binarizes such frequencytransform coefficient information in image information according to twodifferent binarization formats which are a first mode in whicharithmetic encoding is applied and a second mode in which arithmeticencoding is not applied. Likewise, inverse binarizer 244 of decoder 200inverse binarizes such frequency transform coefficient information inimage information according to two different inverse binarizationformats which are a first mode in which arithmetic decoding is appliedand a second mode in which arithmetic decoding is not applied.

Binarizer 132 of encoder 100 may be provided with mode information inthe same manner as switches 134 and 140 of encoder 100. Binarizer 132 ofencoder 100 may obtain given mode information and switch between thebinarization formats for the frequency transform coefficient informationaccording to the mode information.

Likewise, inverse binarizer 244 of decoder 200 may be provided with themode information in the same manner as switches 236 and 242 of decoder200. Inverse binarizer 244 of decoder 200 may obtain the given modeinformation and switch between inverse binarization formats for thefrequency transform coefficient information according to the modeinformation.

For example, different syntax structures are applied to the frequencytransform coefficient information between the first mode and the secondmode.

FIG. 13 is a flowchart indicating a syntax structure according toEmbodiment 1. The syntax structure corresponds to a binarization formatand an inverse binarization format. Binarizer 132 binarizes imageinformation according to the syntax structure indicated in FIG. 13 totransform the image information to a binary data string.

More specifically, binarizer 132 binarizes header information of apicture layer (S101). Next, binarizer 132 binarizes header informationof a slice layer (S102). Next, binarizer 132 binarizes codinginformation of a block layer (S103).

More specifically, binarizer 132 binarizes the coding information of theblock layer other than the frequency transform coefficient information.For example, the frequency transform coefficient information indicatesquantized frequency transform coefficients. In addition, for example,the coding information of the block layer includes prediction parameterinformation. The prediction parameter information indicates a predictionparameter related to a prediction method for an image.

The prediction parameter information may indicate a coding mode which iseither an intra prediction mode or an inter prediction mode. Inaddition, the prediction parameter information may indicate a motionvector and a reference picture which are related to inter prediction. Inaddition, the prediction parameter information may indicate an intraprediction mode related to a prediction direction of the intraprediction.

Binarizer 132 then binarizes, in the first mode (the first mode inS104), frequency transform coefficient information using a syntaxstructure for the first mode (S105). Binarizer 132 then binarizes, inthe second mode (the second mode in S104), frequency transformcoefficient information in a syntax structure for the second mode(S106).

Binarizer 132 then repeats processes (S103 to S106) on each of theblocks included in a slice (S107). Binarizer 132 then repeats processes(S102 to S107) on each of the slices included in a picture (S108).Binarizer 132 then repeats processes (S101 to S108) on each of pictures(S109).

In this way, binarizer 132 binarizes the frequency transform coefficientinformation using different syntaxes between the first mode and thesecond mode, and binarizes the other information using a common syntaxbetween the first mode and the second mode.

In addition, inverse binarizer 244 of decoder 200 inverse binarizesbinary data string according to the syntax structure indicated in FIG.13 to transform the binary data string to image information.

More specifically, inverse binarizer 244 inverse binarizes the binarydata string of the header information of the picture layer (S101). Next,inverse binarizer 244 inverse binarizes the binary data string of theheader information of the slice layer (S102). Next, inverse binarizer244 inverse binarizes the binary data string of coding information in ablock layer (S103). More specifically, inverse binarizer 244 inversebinarizes the binary data string of coding information in the blocklayer other than the binary data string of the frequency transformcoefficient information.

Inverse binarizer 244 then inverse binarizes, in the first mode (thefirst mode in S104), the binary data string of the frequency transformcoefficient information using the syntax structure for the first mode(S105). Inverse binarizer 244 then inverse binarizes, in the second mode(the second mode in S104), the binary data string of the frequencytransform coefficient information using the syntax structure for thesecond mode (S106).

Inverse binarizer 244 then repeats processes (S103 to S106) on each ofthe blocks included in the slice (S107). Inverse binarizer 244 thenrepeats processes (S102 to S107) on each of the slices included in thepicture (S108). Inverse binarizer 244 then repeats processes (S101 toS108) on each of the pictures (S109).

In this way, inverse binarizer 244 inverse binarizes the binary datastring of the frequency transform coefficient information using thedifferent syntax structures between the first mode and the second mode,and inverse binarizes the binary data string of the other informationusing the common syntax structure between the first mode and the secondmode.

In the first mode, arithmetic encoding and arithmetic decoding areapplied. Accordingly, the syntax structure suitable for application ofarithmetic encoding and arithmetic decoding is used as the syntaxstructure for the first mode. For example, the syntax structure for thefirst mode may be a uniform syntax structure for reducing the codingamount in arithmetic encoding, or a simple syntax structure thatrequires a small processing load for binarization.

In the second mode, arithmetic encoding and arithmetic decoding are notapplied. Accordingly, the syntax structure for reducing the codingamount which is required for the binarization itself is used as thesyntax structure for the second mode.

In the example indicated in FIG. 13, the different syntax structuresbetween the first mode and the second mode are applied only to thefrequency transform coefficient information included in imageinformation and indicating the frequency transform coefficients relatedto the frequency components of an image. Subsequently, the common syntaxstructure between the first mode and the second mode is applied to allthe image information other than the frequency transform coefficientinformation. For example, the common syntax structure between the firstmode and the second mode is applied to prediction parameter informationincluded in the image information and indicating prediction parametersrelated to prediction methods for an image.

Although the different syntax structures between the first mode and thesecond mode are applied to only the frequency transform coefficientinformation in the example of FIG. 13, it is to be noted that thedifferent syntax structures between the first mode and the second modemay be applied to the other information. More specifically, thedifferent syntax structures between the first mode and the second modemay be applied to the information part which is included in the imageinformation and including (i) the frequency transform coefficientinformation and (ii) the information which is other than the frequencytransform coefficient information and to which the different syntaxstructures are to be applied. In this case, different syntax structuresare applied also to the information which is other than the frequencytransform coefficient information and to which the different syntaxstructures are to be applied in addition to the frequency transformcoefficient information, according to one of the first mode in whicharithmetic encoding and arithmetic decoding are applied and the secondmode in which arithmetic encoding and arithmetic decoding are notapplied. Thus, compared to the case in which the common syntax structureis applied between the first mode and the second mode, the coding amountof the information which is other than the frequency transformcoefficient information and to which the different syntax structure isto be applied may be reduced in at least one of the first mode and thesecond mode.

In addition, although the common syntax structure is applied to theprediction parameter information between the first mode and the secondmode in the example of FIG. 13, it is to be noted that different syntaxstructures may be applied to some of prediction parameters included inthe prediction parameter information between the first mode and thesecond mode. For example, (i) the common syntax structure may be appliedto any or all of; information related to coding modes; informationrelated to prediction directions in intra prediction; informationrelated to reference pictures in inter prediction; and informationrelated to motion vectors in inter prediction, and (ii) the differentsyntax structures between the first mode and the second mode may beapplied to the parameters other than the prediction parameters to whichthe common syntax structure is applied between the first mode and thesecond mode. In this case, compared to the case in which the commonsyntax structure is applied to the entirety of the prediction parameterinformation between the first mode and the second mode, the codingamount of the prediction parameter information may be reduced in atleast one of the first mode and the second mode.

[A Basic Block]

Binarizer 132 of encoder 100 binarizes a frequency transform block inunits of a basic block. For example, binarizer 132 divides the frequencytransform block into a plurality of basic blocks, and binarizes each ofthe basic blocks. The frequency transform block is a block including aplurality of frequency transform coefficients obtainable throughfrequency transform of a transform unit. In other words, the frequencytransform block corresponds to a transform unit on which frequencytransform has been performed, and can be represented as a frequencytransform coefficient block.

For example, when the transform unit is a block composed of 16×16 pixelvalues, a frequency transform block of 16×16 frequency transformcoefficients is obtained through the frequency transform of thetransform unit. Subsequently, for example, binarizer 132 divides thefrequency transform block having a 16×16 size into a plurality of basicblocks each having a 4×4 size. Subsequently, binarizer 132 binarizes thefrequency transform block having the 16×16 size in units of a basicblock having the 4×4 size.

In addition, more specifically, binarizer 132 binarizes, for each of oneor more basic blocks which constitute the frequency transform block, theplurality of frequency transform coefficients included in the frequencytransform block, according to a predetermined scan order defined in adescending order of frequencies of the one or more basic blocks.

In addition, binarizer 132 binarizes position information indicating theposition of a specific basic block in the frequency transform block inthe second mode. The specific basic block is a basic block including anon-zero coefficient first in the scan order in the one or more basicblocks which constitute the frequency transform block. The non-zerocoefficient is a frequency transform coefficient whose absolute value isnot zero.

Further in the second mode, binarizer 132 binarizes only blockinformation of each of the specific basic block and the following basicblock(s) in the above-described scan order out of the one or more basicblocks which constitute the frequency transform block. The blockinformation indicates the plurality of frequency transform coefficientswhich constitute the basic blocks. It is to be noted that the specificbasic block and the following basic block(s) in the scan order includethe specific basic block and one or more basic blocks which follow thespecific basic block in the scan order.

In this way, encoder 100 is capable of binarizing the positioninformation and the block information as the frequency transformcoefficient information in the second mode. Since encoder 100 binarizesthe block information of each of the specific basic block and the basicblock(s) in the scan order, encoder 100 is capable of assistingreduction in the length of the binary data string of the frequencytransform coefficient information. Encoder 100 is capable of outputtinga bitstream including the binary data string of the frequency transformcoefficient information.

In addition, for example, in the first mode, binarizer 132 may binarizeall of the one or more basic blocks which constitute the frequencytransform block instead of binarizing the position information of thespecific basic block. In this way, binarizer 132 is capable ofbinarizing the frequency transform coefficient information in differentmodes which are the first mode and the second mode.

Likewise, inverse binarizer 244 of decoder 200 inverse binarizes thebinary data string of the frequency transform block in units of a basicblock. More specifically, inverse binarizer 244 of decoder 200 inversebinarizes the binary data string of the plurality of frequency transformcoefficients included in the frequency transform block in units of abasic block according to the above-described scan order.

In addition, for example, in the second mode, inverse binarizer 244 ofdecoder 200 may inverse binarize the binary data string of the positioninformation indicating the position of the specific basic block in thefrequency transform block. Further in the second mode, inverse binarizer244 then inverse binarizes only the binary data string of the blockinformation indicating the plurality of frequency transform coefficientswhich constitute each of the specific basic block and the followingbasic block(s) in the above-described scan order out of the one or morebasic blocks.

In this way, decoder 200 is capable of inverse binarizing the binarydata string of the position information and the block information as thebinary data string of the frequency transform coefficient information inthe second mode. Since decoder 200 inverse binarizes the binary datastring of the block information of each of the specific basic block andthe basic block(s) in the scan order, decoder 200 is capable ofassisting reduction in the length of the binary data string of thefrequency transform coefficient information.

In addition, for example, in the first mode, inverse binarizer 244 mayinverse binarize the binary data string of all of the one or more basicblocks which constitute the frequency transform block instead of inversebinarizing the binary data string of the position information of thespecific basic block. In this way, inverse binarizer 244 is capable ofinverse binarizing the binary data string of the frequency transformcoefficient information in the different modes between the first modeand the second mode.

FIGS. 14A to 14I are each a conceptual diagram indicating one of one ormore basic blocks in a frequency transform block according toEmbodiment 1. Here, the sizes of the frequency transform blocks rangefrom 4×4 to 16×16, and the size of the basic block is 4×4. The sizes andshapes of frequency transform blocks depend on the sizes and shapes oftransform units. The shape of the frequency transform block may be asquare having equal horizontal and vertical lengths, or may be arectangle having unequal horizontal and vertical lengths.

More specifically, FIG. 14A illustrates a single basic block in a 4×4frequency transform block. FIG. 14B illustrates four basic blocks in an8×8 frequency transform block. FIG. 14C illustrates two basic blocks inan 8×4 frequency transform block. FIG. 14D illustrates two basic blocksin an 4×8 frequency transform block. FIG. 14E illustrates sixteen basicblocks in a 16×16 frequency transform block.

FIG. 14F illustrates eight basic blocks in a 16×8 frequency transformblock. FIG. 14G illustrates eight basic blocks in an 8×16 frequencytransform block. FIG. 14H illustrates twelve basic blocks in a 16×12frequency transform block. FIG. 14I illustrates four basic blocks in an4×16 frequency transform block.

The number indicated in each of the one or more basic blocks in each ofFIGS. 14A to 14I indicates the position of the basic block(s) in thefrequency transform block. In this example, the numbers indicating thepositions of the basic blocks in the frequency transform block aredefined in an ascending order of frequencies. In other words, thenumbers indicating the positions of the basic blocks are defined to besmaller as the frequencies of the basic blocks are lower.

It is to be noted that, in the frequency transform block, the partcloser to the upper left corner indicates lower frequencies and the partcloser to the lower right corner indicates higher frequencies. Inaddition, in the frequency transform block, the part closer to the lowerleft corner indicates frequencies which are lower in the horizontaldirection and higher in the vertical direction, and the part closer tothe upper right corner indicates frequencies which are higher in thehorizontal direction and lower in the vertical direction.

In short, the frequency transform coefficients which constitute thetwo-dimensional frequency transform block indicate frequency componentvalues which are higher in the horizontal direction as they are closerto the right end. In other words, the frequency transform coefficientswhich constitute the two-dimensional frequency transform block indicatefrequency component values which are higher in the vertical direction asthey are closer to the lower end.

The frequency levels of a plurality of basic blocks arranged in thedirection toward the lower left end or the upper right end are regardedto be the same. Here, the numbers indicating the positions of theplurality of basic blocks whose frequency levels are the same aredefined in an ascending order of frequencies in the horizontaldirection.

The scan order is defined according to the descending order offrequencies. For example, the scan order is defined according to thedescending order of the numbers indicating the positions of the basicblocks. The basic block whose position is indicated by the largestposition number is assigned at the starting position of the scan order,and the basic block whose position is indicated by the smallest positionnumber is assigned at the ending position of the scan order. In thisexample, the scan order of the plurality of basic blocks whose frequencylevels are the same are defined according to the descending order offrequencies in the horizontal direction.

In each of FIGS. 14A to 14I, the specific basic block is indicated bydiagonal hatching. The specific basic block is a basic block including anon-zero coefficient first in the scan order in the one or more basicblocks which constitute the frequency transform block.

In the second mode, binarizer 132 of encoder 100 binarizes the positioninformation of the specific basic block. In this example, binarizer 132binarizes the number indicating the position of the specific basicblock.

Binarizer 132 then binarizes only block information of each of thespecific basic block and the following basic block(s) in the scan orderout of the one or more basic blocks which constitute the frequencytransform block. In this example, binarizer 132 binarizes the blockinformation of the specific basic block, and binarizes the blockinformation of the basic block whose number is smaller than that of thespecific basic block.

In addition, in the second mode, inverse binarizer 244 of decoder 200inverse binarizes the binary data string of the position information ofthe specific block diagram. In this example, inverse binarizer 244inverse binarizes the binary data string of the number indicating theposition of the specific basic block.

Inverse binarizer 244 then inverse binarizes only block information ofeach of the specific basic block and the following basic block(s) in thescan order out of the one or more basic blocks which constitute thefrequency transform block. In this example, inverse binarizer 244inverse binarizes the binary data string of the block information of thespecific basic block, and inverse binarizes the binary data string ofthe block information of each of at least one basic block which isincluded in the one or more basic blocks and whose number is smallerthan that of the specific basic block.

In this way, encoder 100 and decoder 200 are capable of shortening thebinary data string of the frequency transform coefficient information inthe second mode. Accordingly, encoder 100 and decoder 200 are capable ofpreventing increase in the coding amount in the second mode in whicharithmetic encoding and arithmetic decoding are not applied.

It is to be noted that binarizer 132 may binarize the positioninformation of the specific basic block in the first mode in addition tothe second mode. In the first mode, binarizer 132 may binarize only theblock information of each of the specific basic block and the followingbasic block(s) in the scan order out of the one or more basic blockswhich constitute the frequency transform block.

Likewise, inverse binarizer 244 may inverse binarize the binary datastring of the position information of the specific basic block in thefirst mode in addition to the second mode. In the first mode, inversebinarizer 244 then inverse binarizes only the binary data string of theblock information of each of the specific basic block and the followingbasic block(s) in the scan order out of the one or more basic blockswhich constitute the frequency transform block.

In this way, encoder 100 and decoder 200 are capable of shortening thebinary data string of the frequency transform coefficient informationalso in the first mode. Accordingly, in this way, the coding amount maybe reduced in the first mode in which arithmetic encoding and arithmeticdecoding are applied. In this case, it is to be noted that the samesyntax structure may be applied to the frequency transform coefficientinformation between the first mode and the second mode. Alternatively,different syntax structures may be applied to the frequency transformcoefficient information between the first mode and the second modeaccording to another method.

In addition, the sizes of frequency transform blocks are not limited tothe examples indicated in FIGS. 14A to 14I, and other sizes arepossible. A plurality of sizes may be used as the sizes of a pluralityof frequency transform blocks in a single picture. In addition, thesizes of the basic block is not limited to 4×4, and other sizes arepossible. One or more sizes may be used as the sizes of the plurality ofbasic blocks in the single picture.

FIGS. 14A to 14I each shows the number indicating the position of thebasic block as position information indicating the position of the basicblock. The numbers shown in FIGS. 14A to 14I are examples, and othernumbers based on another standard may be used as the numbers indicatingthe positions of the basic blocks. Alternatively, other informationdifferent from the numbers may be used as the numbers indicating thepositions of the basic blocks.

In addition, when the size of the frequency transform block and the sizeof the basic block are the same, frequency transform coefficientinformation does not always need to include the position information ofthe specific basic block. In other words, when the number of basicblocks included in the frequency transform block is 1, the frequencytransform coefficient information does not always need to include theposition information of the specific basic block. When the number ofbasic blocks included in the frequency transform block is 2, thefrequency transform coefficient information may include the positioninformation of the specific basic block.

In the case of a frequency transform block which does not include anynon-zero coefficient, the frequency transform coefficient informationdoes not always need to include the position information of the specificbasic block in the frequency transform block. In this case, thefrequency transform coefficient information does not always need toinclude the block information indicating a plurality of frequencytransform coefficients which constitute each of the specific basic blockand the following basic block(s). The frequency transform coefficientinformation of the frequency transform block which does not includenon-zero coefficient does not always need to be binarized or encoded.

In addition, binarizer 132 does not always need to binarize thefrequency transform block in units of a basic block in the first mode.In other words, binarizer 132 may binarize the plurality of frequencytransform coefficients included in the frequency transform block in thefirst mode regardless of the basic block.

Likewise, inverse binarizer 244 does not always need to inverse binarizethe binary data string of the frequency transform block in units of abasic block in the first mode. In other words, inverse binarizer 244 mayinverse binarize the binary data string of the plurality of frequencytransform coefficients included in the frequency transform block in thefirst mode regardless of the basic block.

[The Use of a Table in which 0 is not Included as the Number of Non-ZeroCoefficients]

Binarizer 132 of encoder 100 binarizes a data value indicating thenumber of non-zero coefficients included in a basic block as a part offrequency transform coefficient information in the second mode. Also inthe second mode, inverse binarizer 244 of decoder 200 inverse binarizesthe binary data string obtained by binarizing the data value indicatingthe number of non-zero coefficients included in the basic block as thepart of the frequency transform coefficient information. In this way,the plurality of frequency transform coefficients which constitute thebasic block may be represented efficiently.

Binarizer 132 uses a conversion table in which a plurality of datavalues and a plurality of binary values are associated with each otherin the binarization of the data value indicating the number of non-zerocoefficients. Likewise, inverse binarizer 244 uses a conversion table inwhich the plurality of data values and the plurality of binary valuesare associated with each other in the inverse binarization of the datavalue indicating the number of non-zero coefficients. This conversiontable may be represented also as a variable length coding table.

For example, the conversion table may be selected from a plurality oftables which are a table which includes association of a data valueindicating 0 as the number of non-zero coefficients and a table whichdoes not include association of a data value indicating 0 as the numberof non-zero coefficients. In this way, the coding amount of thefrequency transform coefficient information may be reduced.

FIG. 15 is a conceptual diagram indicating two kinds of tables A1 and A2according to Embodiment 1. In each of the two kinds of tables A1 and A2,a plurality of data values and a plurality of binary values areassociated with each other. Each of the plurality of data valuescorresponds to one of a value of trailing_ones and a value of total_coefincluded in a combination.

Parameter trailing_ones indicates the number of non-zero coefficientswhose absolute value is 1 and which continue first in the scan orderaccording to a descending order of frequencies other than the frequencytransform coefficients whose absolute value is 0 in the plurality offrequency transform coefficients included in the basic block. Parametertotal_coef indicates the number of non-zero coefficients in theplurality of frequency transform coefficients included in the basicblock. The combination of trailing_ones and total_coef is an example ofdata values each indicating the number of non-zero coefficients.

Table A1 includes association between the data value indicating 0 as thenumber of non-zero coefficients and a binary value. In other words,table A1 includes the data value in which trailing_ones indicates 0 andtotal_coef indicates 0. Table A2 does not include association betweenthe data value indicating 0 as the number of non-zero coefficients and abinary value. In other words, table A2 does not include data valuesindicating that trailing_ones is 0 and that total_coef is 0.

In this way, the binary value associated with the data value in table A2is defined using a bit length shorter than the bit length of the binaryvalue associated with the same data value in table A1.

In the example of FIG. 15, total_coef is 3, and trailing_ones is 2. Intable A1, “0000101” which is a 7-bit binary value is associated withthese data values, and in table A2, “000011” which is a 6-bit binaryvalue is associated therewith.

For example, binarizer 132 binarizes the data values each indicating thenumber of non-zero coefficients of the basic block having a possibilitythat the number of non-zero coefficients is 0, according to table A1.For example, binarizer 132 binarizes the data values each indicating thenumber of non-zero coefficients of the basic block having no possibilitythat the number of non-zero coefficients is 0, according to table A2.

Likewise, inverse binarizer 244 inverse binarizes the binary valuesobtained by binarizing the data value indicating the number of non-zerocoefficients of the basic block having a possibility that the number ofnon-zero coefficients is 0, according to table A1. Likewise, inversebinarizer 244 inverse binarizes the binary values obtained by binarizingthe data values each indicating the number of non-zero coefficients ofthe basic block having no possibility that the number of non-zerocoefficients is 0, according to table A2.

In this way, encoder 100 and decoder 200 are capable of reducingincrease in the coding amount.

Although the basic block having a 4×4 size is illustrated in FIG. 15, itis to be noted that the size of a basic block may be a size differentfrom 4×4. In addition, the size of a basic block may be the same as thesize of a frequency transform block, or may be smaller than the size ofa frequency transform block. In addition, although a combination oftrailing_ones and total_coef is used as data values each indicating thenumber of non-zero coefficients in this example, it is to be noted thatdata values each indicating the number of non-zero coefficients may beother information.

FIG. 16 is a flowchart indicating selection of a table according toEmbodiment 1. More specifically, FIG. 16 is a flowchart for selecting aconversion table from table A1 and table A2 illustrated in FIG. 15.

For example, binarizer 132 selects a conversion table from table A1 andtable A2 in units of a basic block, and binarizes the data values eachindicating the number of non-zero coefficients included in the basicblock according to the selected transform block. For example, inversebinarizer 244 selects a conversion table from table A1 and table A2 inunits of a basic block, and inverse binarizes the binary values of thedata values each indicating the number of non-zero coefficients includedin the basic block according to the selected transform block.

Here, the basic block which is a current processing target whenbinarization or inverse binarization is performed in units of a basicblock is referred to as a current basic block.

As a precondition, binarizer 132 binarizes the data values eachindicating the number of non-zero coefficients of each of the specificbasic block and the following basic block(s) in the scan order only whenthe specific basic block is included in the frequency transform block.Inverse binarizer 244 then binarizes the data values each indicating thenumber of non-zero coefficients of each of the specific basic block andthe following basic block(s) in the scan order only when the specificbasic block is included in the frequency transform block. The specificbasic block is a basic block including the non-zero coefficient first inthe scan order.

In other words, encoder 100 encodes the frequency transform block whenthe frequency transform block includes a non-zero coefficient, and doesnot encode the frequency transform block when the frequency transformblock does not include any non-zero coefficient. Accordingly, decoder200 decodes the frequency transform block when the frequency transformblock includes a non-zero coefficient, and does not decode the frequencytransform block when the frequency transform block does not include anynon-zero coefficient.

Under the precondition, when the current basic block is not identical tothe frequency transform block (No in S201) and the current basic blockis not a specific basic block (No in S202), table A1 which includesassociation with a data value indicating 0 as the number of non-zerocoefficients is selected (S203). When the current basic block isidentical to the frequency transform block (Yes in S201) or when thecurrent basic block is the specific basic block (Yes in S202), table A2which does not include any association with a data value indicating 0 asthe number of non-zero coefficients is selected (S204).

When the current basic block is identical to the frequency block,whether the data value of the current basic block is binarized isdetermined according to whether the current basic block includes anon-zero coefficient. In this case, the data value of the current basicblock is binarized when the current basic block includes a non-zerocoefficient, and the data value of the current basic block is binarizedwhen the current basic block does not include any non-zero coefficient.

Accordingly, in this case, the current basic block includes a non-zerocoefficient when the data values of the current basic block arebinarized. For this reason, when the current basic block is identical tothe frequency transform block, table A2 which does not include anyassociation with a data value indicating 0 as the number of non-zerocoefficients is selected.

In addition, the specific basic block includes a non-zero coefficient.Accordingly, when the current basic block is the specific basic block,A2 which does not include any association with a data value indicating 0as the number of non-zero coefficients is selected.

It is to be noted that whether the current basic block is identical tothe frequency transform block corresponds to whether the size of thetransform block and the size of the current basic block are the same.For example, when each of basic blocks has a 4×4 size, whether thefrequency transform block has a 4×4 size may be determined instead ofwhether the current basic block is identical to the frequency transformblock.

In addition, the above-described selecting method is an example, andother selecting methods may be used. Alternatively, only one of the twocases in the above-described selecting methods may be used.Alternatively, although a conversion table is selected from the twotables of A1 and A2 in the above example, a conversion table is selectedamong three of more tables including these tables A1 and A2.

Also in the first mode as in the second mode, binarizer 132 may binarizea data value indicating the number of non-zero coefficients according toa conversion table selected from table A2, etc. each of which does notinclude any association with a data value indicating 0 as the number ofnon-zero coefficients. Alternatively, in the first mode, binarizer 132may binarize a data value indicating the number of non-zero coefficientsusing table A1, etc. each of which includes association with a datavalue indicating 0 as the number of non-zero coefficients, without usingtable A2, etc. each of which does not include any association with adata value indicating 0 as the number of non-zero coefficients.

Alternatively, binarizer 132 does not always need to binarize a datavalue indicating the number of non-zero coefficients in the first mode.For example, binarizer 132 may binarize each of a plurality of frequencytransform coefficients in the first mode regardless of the number ofnon-zero coefficients. In the first mode, reduction in the increase inthe coding amount is assisted by application of arithmetic encoding evenwhen the number of non-zero coefficients is not used.

Also in the first mode as in the second mode, inverse binarizer 244 mayinverse binarize a data value indicating the number of non-zerocoefficients according to a conversion table selected from table A2,etc. each of which does not include any association with a data valueindicating 0 as the number of non-zero coefficients. Alternatively, inthe first mode, inverse binarizer 244 may inverse binarize a data valueindicating the number of non-zero coefficients using table A1, etc. eachof which includes association with a data value indicating 0 as thenumber of non-zero coefficients, without using table A2, etc. each ofwhich does not include any association with a data value indicating 0 asthe number of non-zero coefficients.

Alternatively, inverse binarizer 244 does not always need to inversebinarize a binary value of the data value indicating the number ofnon-zero coefficients in the first mode. For example, inverse binarizer244 may inverse binarize each of the plurality of frequency transformcoefficients in the first mode regardless of the number of non-zerocoefficients. In the first mode, reduction in the increase in the codingamount is assisted by application of arithmetic decoding even when thenumber of non-zero coefficients is not used.

[Table Selection Based on the Position of a Basic Block]

A conversion table for binarization and inverse binarization may beselected from a plurality of tables including two or more tables whichare differ from each other in difference between a longest bit lengthand a shortest bit length of a plurality of binary values associatedwith a plurality of data values. In this way, the coding amount of thefrequency transform coefficient information may be reduced.

FIG. 17 is a conceptual diagram indicating four kinds of tables B1 to B4according to Embodiment 1. In each of the four kinds of tables B1 to B4,a plurality of data values and a plurality of binary values areassociated with each other. Each of the plurality of data valuescorresponds to one of a value of trailing_ones and a value of total_coefin a combination. It is to be noted that table B1 in FIG. 17 isidentical to table A1 in FIG. 15.

Specifically, in the example of FIG. 17, total_coef is 3, andtrailing_ones is 2. In table B1, “0000101” which is a 7-bit binary valueis associated with these data values, and in table B3, “01110” which isa 5-bit binary value is associated therewith.

Binarizer 132 of encoder 100 selects a conversion table from amongtables B1 to B4, and binarizer 132 binarizes data values according tothe selected conversion table. Likewise, inverse binarizer 244 ofdecoder 200 selects a conversion table from among tables B1 to B4, andinverse binarizes a binary value of the data value indicating the numberof non-zero coefficients according to the conversion table selected.

It is to be noted that inverse binarizer 244 of decoder 200 selects thesame conversion table as the table selected by binarizer 132 of encoder100 from among tables B1 to B4 according to the same selection standardas that of binarizer 132 of encoder 100.

In addition, in each of tables B1 to B3, the bit length of the binaryvalue associated with a data value indicating the number of non-zerocoefficients is defined to be shorter as the number of non-zerocoefficients is smaller. This tendency is most noticeable in table B1among tables B1 to B3, and least noticeable in table B3. In other words,the bit lengths of a plurality of binary values are most variable intable B1 among tables B1 to B3, and the bit lengths of a plurality ofbinary values are least variable in table B3.

In table B4, the bit lengths of binary values associated with the datavalues each indicating the number of non-zero coefficients are constantregardless of the number of non-zero coefficients. In other words, intable B4, the plurality of binary values associated with the pluralityof data values are defined to have the same bit length. Accordingly, thedifference between the longest bit length and the shortest bit length islargest in table B1, second largest in table B2, third largest in tableB3, and smallest in table B4.

For example, as the number estimated as the number of non-zerocoefficients is smaller, a table having a larger difference between thelongest bit length and the shortest bit length is selected from amongtables B1 to B4. This increases the possibility that a binary valuehaving a shorter bit length is assigned to a data value indicating thenumber of non-zero coefficients.

In contrast, as the number estimated as the number of non-zerocoefficients is larger, a table having a smaller difference between thelongest bit length and the shortest bit length is selected from amongtables B1 to B4. This decreases the possibility that a binary valuehaving a longer bit length is assigned to a data value indicating thenumber of non-zero coefficient.

In addition, it is estimated that the number of non-zero coefficients ina current basic block is affected by the position of the current basicblock in a frequency transform block. In view of this, for example,binarizer 132 of encoder 100 may select a conversion table from amongtables B1 to B4 according to the position of the current basic block inthe frequency transform block. Binarizer 132 may binarize the data valueindicating the number of non-zero coefficients according to the selectedconversion table.

In view of this, for example, inverse binarizer 244 of decoder 200 mayselect a conversion table from among tables B1 to B4 according to theposition of the current basic block in the frequency transform block.Inverse binarizer 244 may binarize the binary value of the data valueindicating the number of non-zero coefficients according to the selectedconversion table. In this way, encoder 100 and decoder 200 are capableof reducing increase in the coding amount.

It is to be noted that, in each of tables B1 to B3, the bit length ofthe binary value is defined to be shorter as trailing_ones is larger.This tendency is most noticeable in table B1 among tables B1 to B3, andleast noticeable in table B3. This tendency is not found in table B4.

There is a correlation between the smallness in the absolute value ofeach frequency transform coefficient in the basic block and thelargeness of trailing_ones. In view of this, as the value estimated asthe absolute value of the frequency transform coefficient is smaller,the table having the most noticeable tendency may be selected from amongtables B1 to B4. This increases the possibility that a binary valuehaving a shorter bit length is assigned to the combination oftrailing_ones and total_coef.

In addition, although FIG. 17 illustrates four kinds of tables B1 to B4,two kinds of tables which are different in longest bit length andshortest bit length may be used, three kinds of tables may be used, orfive kinds of tables may be used.

In addition, the plurality of tables from which a conversion table isselected may include two or more kinds of tables which are the same indifference between the longest bit length and the shortest bit length,in addition to the two or more kinds of tables which are different indifference between the longest bit length and the shortest bit length.In addition, the plurality of tables from which a conversion table isselected may include the two or more kinds of tables which are differentin difference between the longest bit length and the shortest bit lengthand the two or more kinds of tables which are the same in differencebetween the longest bit length and the shortest bit length.

In addition, tables A1 and A2 illustrated in FIG. 15 and tables B1 to B4illustrated in FIG. 17 may be combined. For example, a conversion tablemay be selected from among the plurality of tables B1 to B4 and A2.Furthermore, the plurality of tables from which a conversion table isselected may include new tables obtained by deleting association with adata value indicating 0 as the number of non-zero coefficients fromtables B2 to B4.

In addition, encoder 100 and decoder 200 may select a conversion tablefrom among tables B1 to B4 according to the position of a basic block ina frequency transform block. At that time, encoder 100 and decoder 200may use hierarchical layers of the basic block.

FIGS. 18A to 18I are each a conceptual diagram indicating acorresponding one of hierarchical layers of one of one or more basicblocks in a frequency transform block according to Embodiment 1.

The number indicated in each of the one or more basic blocks in each ofFIGS. 18A to 18I indicates the position of the basic block in thefrequency transform block. In this example, the numbers indicating thepositions of the basic blocks in the frequency transform block aredefined in an ascending order of frequencies. In other words, thenumbers indicating the hierarchical layers of the basic block aredefined to be smaller as the frequency levels corresponding to the basicblock is lower. In short, the hierarchical layers correspond to thefrequency levels.

The frequency levels of the plurality of basic blocks arranged in thedirection toward the lower left end or the upper right end are regardedto be the same. Here, the numbers indicating the hierarchical layers ofthe plurality of basic blocks whose frequency levels are the same aredefined to be the same value.

More specifically, FIG. 18A illustrates a single basic block in a 4×4frequency transform block. FIG. 18B illustrates the hierarchical layersof respective four basic blocks in an 8×8 frequency transform block.FIG. 18C illustrates the hierarchical layers of respective two basicblocks in an 8×4 frequency transform block. FIG. 18D illustrates thehierarchical layers of respective two basic blocks in a 4×8 frequencytransform block. FIG. 18E illustrates the hierarchical layers ofrespective sixteen basic blocks in a 16×16 frequency transform block.

FIG. 18F illustrates the hierarchical layers of respective eight basicblocks in a 16×8 frequency transform block. FIG. 18G illustrates thehierarchical layers of respective eight basic blocks in an 8×16frequency transform block. FIG. 18H illustrates the hierarchical layersof respective twelve basic blocks in a 16×12 frequency transform block.FIG. 18I illustrates the hierarchical layers of respective four basicblocks in a 4×16 frequency transform block.

In addition, the numbers shown in FIGS. 18A to 18I are examples, andother numbers may be used as the numbers indicating the hierarchicallayers of the basic blocks. Alternatively, other information which isdifferent in format from the numbers may be used as informationindicating the hierarchical layers of the basic blocks.

FIG. 19 is a flowchart indicating a pattern determination processingaccording to Embodiment 1. For example, binarizer 132 of encoder 100determines a pattern according to the position of a current basic blockin a frequency transform block, and selects a conversion table accordingto the determined pattern. This pattern corresponds to the position ofthe current basic block in the frequency transform block, andcorresponds to the method for selecting the conversion table.

For this reason, binarizer 132 of encoder 100 determines whether apreceding basic block is present in the same hierarchical layer in whichthe current basic block is present (S301). Here, the preceding basicblock is a basic block that precedes the current basic block in a scanorder. When determining that the preceding basic block is present in thesame hierarchical layer in which the current basic block is present (Yesin S301), binarizer 132 determines a current pattern to be a firstpattern (S302).

When determining that the preceding basic block is not present in thesame hierarchical layer in which the current basic block is present (Noin S301), binarizer 132 determines whether a specific basic block ispresent in a higher hierarchical layer than the current basic block(S303). Here, the specific basic block is a basic block including anon-zero coefficient first in the scan order in the one or more basicblocks which constitute the frequency transform block.

When determining that a specific basic block is present in a higherhierarchical layer than the current basic block (Yes in S303), binarizer132 determines a current pattern as a second pattern (S304). Whendetermining that no specific basic block is present in a higherhierarchical layer than the current basic block (No in S303), binarizer132 determines a current pattern as a third pattern (S305).

It is to be noted that the first pattern, the second pattern, and thethird pattern are examples of patterns. Only some of the first pattern,the second pattern, and the third pattern may be used, or other patternsmay be used.

In the same manner as binarizer 132 of encoder 100, inverse binarizer244 of decoder 200 determines a pattern and selects a conversion table.Accordingly, as for the determination of the pattern and selection ofthe conversion table, the operations performed by binarizer 132 ofencoder 100 may be replaced with the operations performed by inversebinarizer 244 of decoder 200. The same applies to the followingdescriptions.

FIG. 20A is a conceptual diagram illustrating a current basic blockhaving a first pattern according to Embodiment 1. When a preceding basicblock is present in the same hierarchical layer in which the currentbasic block is present, the pattern corresponding to the position of thecurrent basic block is determined as the first pattern.

In other words, when the current basic block is located at the positionin the same hierarchical layer in which the preceding basic block ispresent, the current pattern is determined to be the first pattern. Forexample, when the current basic block is located in any of thediagonally hatched parts in FIG. 20A, the pattern corresponding to theposition of the current basic block is determined to be the firstpattern.

FIG. 20B is a conceptual diagram illustrating a current basic blockhaving a second pattern according to Embodiment 1. When a precedingbasic block is present in the same hierarchical layer in which thecurrent basic block is present and a specific basic block is present ina higher hierarchical layer than the current basic block, the patterncorresponding to the position of the current basic block is determinedas the second pattern.

In other words, when the current basic block is not located at theposition in the same hierarchical layer in which the preceding basicblock is present and the specific basic block is present in a higherhierarchical layer than the current basic block, the current pattern isdetermined to be the second pattern. For example, when the current basicblock is located at any of the diagonally hatched parts in FIG. 20B, thepattern corresponding to the position of the current basic block isdetermined to be the second pattern.

FIG. 20C is a conceptual diagram illustrating a current basic blockhaving a third pattern according to Embodiment 1. When no precedingbasic block is present in the same hierarchical layer in which thecurrent basic block is present and no specific basic block is present ina higher hierarchical layer than the current basic block, the patterncorresponding to the position of the current basic block is determinedas the third pattern.

In other words, when the current basic block is not located at theposition in the same hierarchical layer in which the preceding basicblock is present and no specific basic block is present in a higherhierarchical layer than the current basic block, the current pattern isdetermined to be the third pattern. For example, when the current basicblock is located at any of the diagonally hatched parts in FIG. 20C, thepattern corresponding to the position of the current basic block isdetermined to be the third pattern.

FIG. 21 is a relationship diagram indicating tables to be selected inthe first pattern according to Embodiment 1. For example, binarizer 132of encoder 100 predicts the number of non-zero coefficients included inthe current basic block, and selects a conversion table from amongtables B1 to B4 according to the prediction value indicating the numberof non-zero coefficients included in the current basic block. Thisprediction value is also represented as nC.

In the example of FIG. 21, binarizer 132 selects table B1 having thelargest difference between the longest bit length and the shortest bitlength as a conversion table when the prediction value ranges from 0 to1.

In addition, when the prediction value ranges from 2 to 3, binarizer 132selects table B2 having the second largest difference between thelongest bit length and the shortest bit length as a conversion table. Inaddition, when the prediction value ranges from 4 to 7, binarizer 132selects table B3 having the third largest difference between the longestbit length and the shortest bit length as a conversion table. Inaddition, when the prediction value ranges from 8 to 16, binarizer 132selects table B4 having the smallest difference between the longest bitlength and the shortest bit length as a conversion table.

In the first pattern, a preceding basic block is present in the samehierarchical layer in which the current basic block is present.Accordingly, binarizer 132 predicts the number of non-zero coefficientsincluded in the current basic block according to the number of non-zerocoefficients included in the preceding basic block present in the samehierarchical layer in which the current basic block is present. Morespecifically, binarizer 132 predicts the number of non-zero coefficientsincluded in the preceding basic block present in the same hierarchicallayer in which the current basic block is present, as the number ofnon-zero coefficients included in the current basic block.

In the first pattern, when the current basic block is a specific basicblock which includes a non-zero coefficient first in a scan order, thenumber of non-zero coefficients included in a preceding basic block is0. Accordingly, binarizer 132 predicts 0 as the number of non-zerocoefficients included in the current basic block.

In addition, when a plurality of preceding basic blocks are present inthe same hierarchical layer in which the current basic block is present,binarizer 132 may predict the number of non-zero coefficients includedin the current basic block according to the number of non-zerocoefficients included in the preceding basic block located immediatelybefore the current basic block in the scan order.

Binarizer 132 then predicts the number of non-zero coefficients in thebasic block according to the number of non-zero coefficients in thepreceding basic block, and selects a conversion table from among tablesB1 to B4 according to the prediction value indicating the number ofnon-zero coefficients. In other words, binarizer 132 selects aconversion table from among tables B1 to B4 according to the number ofnon-zero coefficients in the preceding basic block.

It is to be noted that FIG. 21 illustrates examples of prediction valueranges and tables to be selected. Prediction value ranges and tables tobe selected are not limited to the examples illustrated in FIG. 21. Inaddition, binarizer 132 may select a conversion table according to notonly the prediction value indicating the number of non-zero coefficientsbut also a combination of the prediction value indicating the number ofnon-zero coefficients and other information. This also applies to theother patterns in addition to the first pattern.

FIG. 22 is a relationship diagram indicating tables to be selected inthe second pattern according to Embodiment 1.

In the second pattern, no preceding basic block is present in the samehierarchical layer in which a current basic block is present. However, abasic block including a non-zero coefficient is present in a higherhierarchical layer than the layer in which the current basic block ispresent, that is, at a higher frequency level than the frequency levelat the position of the current basic block. In this case, binarizer 132predicts the number of non-zero coefficients included in the currentbasic block is large, and increases the prediction value indicating thenumber of non-zero coefficients included in the current basic block.Binarizer 132 then selects a conversion table according to the increasedprediction value.

For example, binarizer 132 determines the prediction value indicatingthe number of non-zero coefficients included in the current basic blockas the largest value of the number of non-zero coefficients. Binarizer132 then selects a conversion table according to the prediction valuedetermined as the largest value of the number of non-zero coefficients.

For example, binarizer 132 determines the prediction value indicatingthe number of non-zero coefficients included in the current basic block,to be 16 which is the largest value of the number of non-zerocoefficients. Binarizer 132 then selects a conversion table according tothe prediction value determined to be 16 as the largest value of thenumber of non-zero coefficients. In this way, binarizer 132 selectstable B4 having the smallest difference between the longest bit lengthand the shortest bit length as a conversion table.

It is to be noted that, in the second pattern, binarizer 132 does notalways need to determine the prediction value as the largest value, andmay determine a prediction value which is a predetermined value largerthan an average value of the numbers of non-zero coefficients. Binarizer132 may then select a table having a difference between the longest bitlength and the shortest bit length smaller than the average differenceas a conversion table from among tables B1 to B4.

FIG. 23 is a relationship diagram indicating tables to be selected for afrequency transform around a current frequency transform block in thethird pattern according to Embodiment 1. In this example, binarizer 132of encoder 100 selects a conversion table according to the number ofnon-zero coefficients included in the frequency transform around thecurrent frequency transform block in the third pattern.

In the third pattern, a preceding basic block is present in the samehierarchical layer in which the current basic block is present. Inaddition, no specific basic block is present in any hierarchical layerhigher than the hierarchical layer in which the current basic block ispresent. In view of this, binarizer 132 predicts the number of non-zerocoefficients included in the current basic block according to the numberof non-zero coefficients included in the frequency transform blockaround the current frequency transform block. Binarizer 132 may predictthe number of non-zero coefficients included in the frequency transformblock around the current frequency transform block as the number ofnon-zero coefficients included in the current basic block.

Binarizer 132 then selects a conversion table from among tables B1 to B4according to the prediction value indicating the number of non-zerocoefficients included in the current basic block. In other words,binarizer 132 selects the conversion table from among tables B1 to B4according to the number of non-zero coefficients which can be includedin the frequency transform block around the current frequency transformblock.

For example, the frequency transform block around the current frequencytransform block is a frequency transform block which is spatially closeto the frequency transform block including the current basic block, andwhich has been encoded successfully. Hereinafter, a transform blockincluding the current basic block is referred to as a current frequencytransform block, and a frequency transform block around the currentfrequency transform block is referred to as a neighboring frequencytransform block. The neighboring frequency transform block may be afrequency transform block spatially located in a predetermined rangefrom the current frequency transform block.

In addition, the neighboring frequency transform block may be afrequency transform block adjacent to the left of or above the currentfrequency transform block. In this way, binarizer 132 is capable ofpredicting the number of non-zero coefficients at high accuracyaccording to the number of non-zero coefficients included in thefrequency transform block close to the current frequency transformblock.

In addition, the neighboring frequency transform block may be afrequency transform block which is encoded immediately before in codingorder. This enables simple prediction of the number of non-zerocoefficients and reduction in memory capacity for storing informationrelated to the number of non-zero coefficients.

In addition, the neighboring frequency transform block may be afrequency transform block which is in a predetermined range from thecurrent frequency transform block and whose coding mode is the same asthat of the current frequency transform block. In this way, binarizer132 is capable of predicting the number of non-zero coefficients at highaccuracy according to the frequency transform block whose tendency ofoccurrence of non-zero coefficients is estimated to be similar to thatof the current frequency transform block. It is to be noted that thepredetermined range may be a range of a coding tree unit including thecurrent frequency transform block.

The following number is used as the number of non-zero coefficientsincluded in the neighboring frequency transform block: the number ofnon-zero coefficients included in a basic block whose position relativeto the neighboring frequency transform block is equivalent to theposition of the current basic block relative to the current frequencytransform block. In this way, binarizer 132 is capable of predicting thenumber of non-zero coefficients at high accuracy according to the basicblock having a strong correlation with the current basic block in termsof the number of non-zero coefficients.

The number of non-zero coefficients of the entirety of the neighboringfrequency transform block may be used as the number of non-zerocoefficients included in the neighboring frequency transform block. Inthis way, the information is integrated regardless of the size offrequency transform block. This enables simple prediction of the numberof non-zero coefficients and reduction in memory capacity for storinginformation related to the number of non-zero coefficients.

In addition, binarizer 132 may derive the number of non-zerocoefficients per basic block according to the number of non-zerocoefficients of the entirety of the neighboring frequency transformblock, and predict the number of non-zero coefficients included in thecurrent basic block according to the number of non-zero coefficients perbasic block. In this way, binarizer 132 is capable of appropriatelypredicting the number of non-zero coefficients regardless of differencein size of a frequency transform block. Binarizer 132 is capable ofselecting a conversion table according to the appropriate predictionvalue.

FIG. 24 is a relationship diagram indicating tables to be selectedaccording to the coding mode in the third pattern according toEmbodiment 1. In this example, binarizer 132 selects a conversion tableaccording to the coding mode which is either an inter prediction mode oran intra prediction mode instead of the number of non-zero coefficientsincluded in the neighboring frequency transform block in the thirdpattern. This coding mode corresponds to one of the inter prediction andintra prediction which is used for encoding and decoding of the currentbasic block.

For example, when the coding mode for the current block is an interprediction mode, it is estimated that the prediction accuracy is highand the number of non-zero coefficients is small compared to those inintra prediction. Accordingly, binarizer 132 selects table B1 having alarge difference between the longest bit length and the shortest bitlength. When the coding mode for the current block is an intraprediction mode, it is estimated that the prediction accuracy is low andthe number of non-zero coefficients is large compared to those in interprediction. Accordingly, binarizer 132 selects table B2 having a smallerdifference between the longest bit length and the shortest bit lengththan table B1.

It is to be noted that FIG. 24 illustrates examples of tables to beselected. The tables to be selected are not limited to the examplesillustrated in FIG. 24. In addition, binarizer 132 may select aconversion table according to not only the coding mode but also acombination of the coding mode and other information.

FIG. 25 is a relationship diagram indicating tables to be selectedaccording to quantization parameters in the third pattern according toEmbodiment 1. In this example, binarizer 132 selects, in the thirdpattern, a conversion table according to a quantization parameter (QP)value instead of the number of non-zero coefficients included in theneighboring frequency transform block and the coding mode which iseither an inter prediction mode or an intra prediction mode. This QPvalue is a value of a quantization parameter which is used for encodingand decoding of the current basic block. The quantization width islarger when the QP value is larger.

For example, as the QP value is larger, it is estimated that the valueof a frequency transform coefficient is likely to be quantized to 0, andthat the number of non-zero coefficients which are generated throughquantization is small. Accordingly, binarizer 132 selects a table havinga larger difference between the longest bit length and the shortest bitlength from among tables B1 to B4 as the QP value is larger.

In contrast, as the QP value is small, it is estimated that the value ofa frequency transform coefficient is unlikely to be quantized to 0, andthat the number of non-zero coefficients which are generated throughquantization is large. Accordingly, binarizer 132 selects a table havinga small difference between the longest bit length and the shortest bitlength from among tables B1 to B4 as the QP value is small.

In addition, when the QP value ranges from 0 to 21, binarizer 132selects table B4 having the smallest difference between the longest bitlength and the shortest bit length as a conversion table.

In addition, when the QP value ranges from 22 to 31, binarizer 132selects table B3 having the second smallest difference between thelongest bit length and the shortest bit length as a conversion table. Inaddition, when the QP value ranges from 32 to 41, binarizer 132 selectstable B2 having the third smallest difference between the longest bitlength and the shortest bit length as a conversion table. In addition,when the QP value ranges from 42 to 51, binarizer 132 selects table B1having the largest difference between the longest bit length and theshortest bit length as a conversion table.

It is to be noted that FIG. 25 illustrates examples of QP value rangesand tables to be selected. QP value ranges and tables to be selected arenot limited to the examples illustrated in FIG. 25. In addition,binarizer 132 may select a conversion table according to not only the QPvalue but also a combination of the QP value and other information.

In addition, in the above-described example, binarizer 132 determines atable selecting method according to the position of the current basicblock, and selects a conversion table according to the determined tableselecting method. In this way, binarizer 132 selects the conversiontable according to the position of the current basic block.

When the position of the current basic block is closer to the upper leftcorner of the frequency transform block, it is estimated that the numberof non-zero coefficients included in the current basic block is larger.Accordingly, binarizer 132 may select, as a conversion table, a tablehaving a smaller difference between the longest bit length and theshortest bit length from among tables B1 to B4, etc. as the position ofthe current basic block is closer to the upper left corner of thefrequency transform block. In this way, binarizer 132 selects theconversion table according to the position of the current basic block.

In the above description, the term “prediction” is used to explain thatthe number of non-zero coefficients is predicted, but the term“estimation” may be used instead of “prediction” in order to distinguishfrom image prediction such as intra prediction, inter prediction, etc.

[A Syntax Structure of Frequency Transform Coefficient Information]

FIG. 26 is a data diagram indicating a syntax structure according toEmbodiment 1. Binarizer 132 of encoder 100 binarizes frequency transformcoefficient information according to the syntax structure indicated inFIG. 26. Inverse binarizer 244 of decoder 200 inverse binarizes a binarydata string of the frequency transform coefficient information accordingto the syntax structure indicated in FIG. 26.

The example of FIG. 26 is an example in the case of a basic block havinga 4×4 size, but the size of the basic block is not limited to 4×4. Inaddition, the size of a basic block may be the same as the size of afrequency transform block, or may be smaller than the size of afrequency transform block. In addition, the parameters indicated in boldin FIG. 26 are parameters described in a binary data string.

Parameter last_sub_block_pos is information indicating the position of aspecific basic block. The specific basic block is a basic blockincluding a non-zero coefficient first in a scan order of the one ormore basic blocks which constitute a frequency transform block. The scanorder is defined in a descending order of frequencies of the one or morebasic blocks. The last_sub_block_pos may be information indicating, as anumber, the position of the specific basic block, for example, asindicated in FIGS. 14A to 14I. The binary data string includes at mostone last_sub_block_pos for each frequency transform block.

Parameter coef_token is information indicating the number of non-zerocoefficients included in a basic block. Specifically, coef_tokencorresponds to both total_coef and trailing_ones. More specifically,coef_token may be a binary value corresponding to the data valueobtained by combining total_coef and trailing_ones, for example, asindicated in FIG. 15 and FIG. 17. The binary data string includes atmost one coef_token for each basic block.

Parameter total_zeros is information indicating a total number of zerocoefficients which appear after the non-zero coefficient appeared firstin the scan order defined in the descending order of frequencies of aplurality of frequency transform coefficients included in the one ormore basic blocks. Here, the non-zero coefficient is a frequencytransform coefficient whose value is zero. The binary data stringincludes at most one total_zeros for each basic block.

Parameter run_before is information indicating the number of zerocoefficients which appeared in sequence after each of non-zerocoefficients which appeared in the scan order defined in the descendingorder of frequencies indicated by the plurality of frequency transformcoefficients included in the one or more basic blocks. The binary datastring includes a certain number of parameters run_before. The certainnumber is at most the number obtained by subtracting 1 from the numberof non-zero coefficients.

Parameter coeff_sign_flag is information indicating whether the value ofeach non-zero coefficient included in the basic block is positive ornegative. The binary data string includes a certain number of parameterscoeff_sign_flag. The certain number is at most the same number as thenumber of non-zero coefficients.

Parameter coeff_abs_level_remaining is information indicating theabsolute value of each non-zero coefficient included in the basic block.The binary data string includes a certain number of parameterscoeff_abs_level_remaining. The certain number is at most the same numberas the number of non-zero coefficients.

The syntax structure indicated in FIG. 26 is an example. Another syntaxstructure which is different from the syntax structure indicated in FIG.26 but indicates information similar to the information indicated by thesyntax structure in FIG. 26 may be used.

[A Mounting Example of the Encoder]

FIG. 27 is a block diagram illustrating a mounting example of encoder100 according to Embodiment 1. Encoder 100 includes circuitry 160 andmemory 162. For example, a plurality of constituent elements of encoder100 illustrated in FIG. 1 and FIG. 11 are mounted as circuitry 160 andmemory 162 illustrated in FIG. 27.

Circuitry 160 is circuitry for performing information processing andaccessible to memory 162. For example, circuitry 160 is an exclusive orgeneral electronic circuit for encoding image information. Circuitry 160may be a processor such as a CPU. Alternatively, circuitry 160 may be anassembly of a plurality of electronic circuits. In addition, forexample, circuitry 160 may take the roles of two or more of theconstituent elements other than the constituent elements for storinginformation among the plurality of constituent elements of encoder 100illustrated in FIG. 1 and FIG. 11.

Memory 162 is general memory or exclusive memory in which informationused by circuitry 160 to encode image information is stored. Memory 162may be an electronic circuit, or may be connected to circuitry 160.Alternatively, memory 162 may be an assembly of a plurality ofelectronic circuits. In addition, memory 162 may be a magnetic disc, anoptical disc, or the like, or may be represented as storage, a recordingmedium, or the like. In addition, memory 162 may be non-volatile memory,or volatile memory.

For example, in memory 162, image information to be encoded may bestored or a bitstream corresponding to encoded image information may bestored. In addition, a program that is executed by circuitry 160 toencode image information may be stored in memory 162.

In addition, for example, circuitry 160 may take the roles of theconstituent elements for storing information among the plurality ofconstituent elements of encoder 100 illustrated in FIG. 1 and FIG. 11.Specifically, memory 162 may take the roles of block memory 118 andframe memory 122 illustrated in FIG. 1, or the role of intermediatebuffer 136 illustrated in FIG. 11.

It is to be noted that, in encoder 100, not all the plurality ofconstituent elements illustrated in FIG. 1 and FIG. 11, etc. may bemounted, or not all the plurality of processes described above may beperformed. Part of the plurality of constituent elements illustrated inFIG. 1 and FIG. 11, etc. may be included in one or more other devices,and part of the plurality of processes described above may be performedby the one or more other devices.

In encoder 100, part of the plurality of constituent elementsillustrated in FIG. 1 and FIG. 11, etc. may be mounted, and thefrequency transform coefficient information may be encoded appropriatelyby means of part of the above-described processes being executed.

[An Example of a First Encoding Operation Performed by the Encoder]

FIG. 28 is a flowchart indicating an example of a first encodingoperation performed by encoder 100 according to Embodiment 1. Forexample, circuitry 160 of encoder 100 illustrated in FIG. 27 encodesimage information and outputs a bitstream in which the image informationis encoded, by performing the operation indicated in FIG. 28.

Specifically, circuitry 160 binarizes the image information first(S401). For example, the image information includes frequency transformcoefficient information related to the frequency components of theimage, prediction parameter information related to prediction methodsfor the image, and so on. Circuitry 160 switches whether or not to applyarithmetic encoding to the binary data string in which the imageinformation has been binarized (S402).

When arithmetic encoding is applied to the binary data string (Yes inS402), circuitry 160 applies arithmetic encoding to the binary datastring, and outputs a bitstream including the binary data string towhich arithmetic encoding has been applied (S403).

When arithmetic encoding is not applied to the binary data string (No inS402), circuitry 160 skips applying arithmetic encoding to the binarydata string, and outputs a bitstream including the binary data string towhich arithmetic encoding has not been applied (S404).

In this way, encoder 100 is capable of skipping arithmetic encoding.Accordingly, encoder 100 is capable of supporting reduction inprocessing delay generated by the arithmetic encoding.

FIG. 29 is a flowchart indicating an example of a first encodingoperation performed by encoder 100 according to Embodiment 1. In otherwords, FIG. 29 indicates a specific example of binarization processing(S401) in FIG. 28.

Circuitry 160 binarizes other information different from the frequencytransform coefficient information included in the image information,according to the binarization format which is common between whenarithmetic encoding is applied to the binary data string and whenarithmetic encoding is not applied to the binary data string (S411). Theother information includes, for example, a part or the entirety ofprediction parameter information.

In addition, circuitry 160 binarizes the frequency transform coefficientinformation included in the image information, according to binarizationformats which are different between when arithmetic encoding is appliedto the binary data string and when arithmetic encoding is not applied tothe binary data string (S412). More specifically, circuitry 160 maybinarize the frequency transform coefficient information included in theimage information, according to binarization formats which are differentbetween when arithmetic encoding is applied to the binary data stringand when arithmetic encoding is not applied to the binary data string.

In this way, encoder 100 is capable of appropriately binarizing thefrequency transform coefficient information which largely affects thetotal coding amount, according to whether or not arithmetic encoding isapplied. Accordingly, encoder 100 is capable of appropriately encodingthe frequency transform coefficient information, thereby being able toreduce increase in the total coding amount.

It is to be noted that the processing order of the binarization of theother information (S411) and the binarization of the frequency transformcoefficient information (S412) may be inversed.

In addition, for example, the prediction parameter information includes:information related to encoding modes; information related to predictiondirections in intra prediction; information related to referencepictures in inter prediction; and information related to motion vectorsin inter prediction.

Circuitry 160 may binarize these kinds of information included in theprediction parameter information, according to the binarization formatwhich is common between when arithmetic encoding is applied to thebinary data string and when arithmetic encoding is not applied to thebinary data string. Alternatively, circuitry 160 may binarize at leastone of these kinds of information, according to the binarization formatwhich is common between when arithmetic encoding is applied to thebinary data string and when arithmetic encoding is not applied to thebinary data string.

In addition, circuitry 160 may binarize only the frequency transformcoefficient information included in the image information, according tothe binarization formats which are different depending on whetherarithmetic encoding is applied. Circuitry 160 may binarizes all theinformation other than the frequency transform coefficient informationincluded in the image information, according to the binarization formatwhich is common regardless of whether arithmetic encoding is applied.

In this way, encoder 100 is capable of binarizing all the informationother than the frequency transform coefficient information, according tothe common binarization format. Accordingly, the processing issimplified.

FIG. 30 is a flowchart indicating binarization processing of frequencytransform coefficient information in an example of a first encodingoperation performed by encoder 100 according to Embodiment 1. In otherwords, FIG. 30 indicates a specific example of binarization processing(S412) of frequency transform coefficient information in FIG. 29.

When arithmetic encoding is applied to a binary data string (Yes inS421), circuitry 160 binarizes frequency transform coefficientinformation according to a first binarization format (S422). Whenarithmetic encoding is not applied to a binary data string (No in S421),circuitry 160 binarizes frequency transform coefficient informationaccording to a second binarization format (S423). When arithmeticencoding is not applied to the binary data string, circuitry 160binarizes the frequency transform coefficient information according to abinarization format which generates a smaller number of bits whenarithmetic encoding is not applied to the binary data string than whenarithmetic encoding is applied to the binary data string.

In this way, encoder 100 is capable of assisting reduction in codingamount of the frequency transform coefficient information whenarithmetic encoding is not applied.

[An Example of a Second Encoding Operation Performed by the Encoder]

FIG. 31 is a flowchart indicating an example of a second encodingoperation performed by encoder 100 according to Embodiment 1. Forexample, circuitry 160 of encoder 100 illustrated in FIG. 27 encodesimage information by performing the operation indicated in FIG. 31.

Specifically, circuitry 160 encodes position information indicating theposition of the specific basic block (S501). The specific basic block isa basic block including, as one of a plurality of frequency transformcoefficients, a non-zero coefficient first in the scan order in the oneor more basic blocks which constitute the frequency transform blockincluding the plurality of frequency transform coefficients.

Circuitry 160 encodes only block information indicating the plurality offrequency transform coefficients which constitute each of the specificbasic block and the following basic block(s) in the predetermined scanorder out of the one or more basic blocks which constitute the frequencytransform block (S502).

In this way, encoder 100 is capable of binarizing the positioninformation and the block information as the frequency transformcoefficient information. Since encoder 100 encodes the block informationof each of the specific basic block and the following basic block(s) inthe predetermined scan order, encoder 100 is capable of assistingreduction in the coding amount of the frequency transform coefficientinformation.

It is to be noted that circuitry 160 may encode position informationonly when the number of one or more basic blocks which constitute afrequency transform block is two or more. In this way, when, forexample, the size of the frequency transform block and the size of eachbasic block are the same, encoder 100 is capable of assisting furtherreduction in coding amount of the frequency transform coefficientinformation.

In addition, circuitry 160 may encode position information and blockinformation only when a specific basic block is present in a frequencytransform block. In this way, when, for example, the size of thefrequency transform block and the size of each basic block are the same,encoder 100 is capable of assisting further reduction in coding amountof the frequency transform coefficient information.

In addition, circuitry 160 may encode image information and output abitstream in which the image information has been encoded, in the samemanner as in the example of a first encoding operation. For example,circuitry 160 binarizes image information as in FIG. 28 (S401).Circuitry 160 then switches whether or not to apply arithmetic encodingto the binary data string in which the image information has beenbinarized (S402).

When arithmetic encoding is applied to the binary data string (Yes inS402), circuitry 160 applies arithmetic encoding to the binary datastring, and outputs a bitstream including the binary data string towhich arithmetic encoding has been applied (S403). When arithmeticencoding is not applied to the binary data string (No in S402),circuitry 160 skips applying arithmetic encoding to the binary datastring, and outputs a bitstream including the binary data string towhich arithmetic encoding has not been applied (S404).

In addition, as indicated in FIG. 29, circuitry 160 binarizes otherinformation included in the image information, according to thebinarization format which is common between when arithmetic encoding isapplied to the binary data string and when arithmetic encoding is notapplied to the binary data string (S411). The other informationincludes, for example, a part or the entirety of prediction parameterinformation.

In addition, circuitry 160 then binarizes the frequency transformcoefficient information included in the image information, according tobinarization formats different between when arithmetic encoding isapplied to the binary data string and when arithmetic encoding is notapplied to the binary data string (S412).

In addition, when arithmetic encoding is not applied to the binary datastring, circuitry 160 binarizes the frequency transform coefficientinformation including the position information and the blockinformation, to encode the position information and the blockinformation. Here, the block information which is encoded is the blockinformation of the specific basic block and the following basic block(s)in the predetermined scan order. In this way, encoder 100 is capable ofassisting reduction in coding amount of the frequency transformcoefficient information when arithmetic encoding is not applied.

[An Example of a Third Encoding Operation Performed by the Encoder]

FIG. 32 is a flowchart indicating an example of a third encodingoperation performed by encoder 100 according to Embodiment 1. Forexample, circuitry 160 of encoder 100 illustrated in FIG. 27 encodesimage information by performing the operation indicated in FIG. 32.

Specifically, circuitry 160 binarizes a data value indicating the numberof non-zero coefficients included in a current basic block according toa conversion table in which a plurality of data values and a pluralityof binary values are associated with each other, to encode the imageinformation including the data value (S601). Here, the current basicblock is one of the one or more basic blocks which constitute thefrequency transform block including the plurality of frequency transformcoefficients.

In this way, encoder 100 is capable of appropriately encodingsignificant information which is used for efficient representation ofthe plurality of frequency transform coefficients which constitute thebasic block.

FIG. 33 is a flowchart indicating binarization processing in an exampleof a third encoding operation performed by encoder 100 according toEmbodiment 1. In other words, FIG. 33 indicates a specific example ofbinarization processing in FIG. 32.

Circuitry 160 selects a conversion table from a plurality of tablesincluding a first table which includes association with a data valueindicating 0 as the number of non-zero coefficients and a second tablewhich does not include any association with a data value indicating 0 asthe number of non-zero coefficients (S611). Circuitry 160 then binarizesthe data value according to the selected conversion table (S612).

In this way, encoder 100 is capable of using the table having a reducedinformation amount as the conversion table for binarization. In thisway, encoder 100 is capable of assisting reduction in coding amount ofthe frequency transform coefficient information.

Circuitry 160 may binarize only the data value indicating the number ofnon-zero coefficients included in each of the specific basic block andthe following basic block(s) in the predetermined scan order among theone or more basic blocks which constitute the frequency transform block.In other words, circuitry 160 may binarize the data value indicating thenumber of non-zero coefficients of each of the specific basic block andthe following basic block(s) in the predetermined scan order, as thedata value indicating the number of non-zero coefficients of a currentbasic block.

In this way, encoder 100 is capable of assisting reduction in codingamount of the frequency transform coefficient information. It is to benoted that the specific basic block is a basic block including anon-zero coefficient first in the scan order which is defined in adescending order of frequencies in the one or more basic blocks whichconstitute the frequency transform block including a plurality offrequency transform coefficients, as one of the plurality of frequencytransform coefficients.

In addition, circuitry 160 may binarize the data value indicating thenumber of non-zero coefficients of the current basic block only when aspecific basic block is included in the one or more basic blocks whichconstitute the frequency transform block. When the frequency transformblock and the current basic block are the same, circuitry 160 may thenselect, as the conversion table, the second table which does not includeany association with a data value indicating 0 as the number of non-zerocoefficients.

In this way, when, for example, the size of the frequency transformblock and the size of each basic block are the same, encoder 100 iscapable of assisting further reduction in coding amount of the frequencytransform coefficient information, using the second table which does notinclude any association with a data value indicating 0 as the number ofnon-zero coefficient.

In addition, when the current basic block is a specific basic block,circuitry 160 may select, as the conversion table, the second tablewhich does not include any association with a data value indicating 0 asthe number of non-zero coefficients.

In this way, when, for example, the current basic block is a specificbasic block, encoder 100 is capable of assisting further reduction incoding amount of the frequency transform coefficient information, usingthe second table which does not include any association with a datavalue indicating 0 as the number of non-zero coefficients.

In addition, circuitry 160 may encode image information and output abitstream in which the image information has been encoded, in the samemanner as in the example of a first encoding operation. For example,circuitry 160 binarizes image information as in FIG. 28 (S401).Circuitry 160 then switches whether or not to apply arithmetic encodingto the binary data string in which the image information has beenbinarized (S402).

When arithmetic encoding is applied to the binary data string (Yes inS402), circuitry 160 applies arithmetic encoding to the binary datastring, and outputs a bitstream including the binary data string towhich arithmetic encoding has been applied (S403). When arithmeticencoding is not applied to the binary data string (No in S402),circuitry 160 skips applying arithmetic encoding to the binary datastring, and outputs a bitstream including the binary data string towhich arithmetic encoding has not been applied (S404).

In addition, as indicated in FIG. 29, circuitry 160 binarizes otherinformation included in the image information, according to thebinarization format which is common between when arithmetic encoding isapplied to the binary data string and when arithmetic encoding is notapplied to the binary data string (S411). The other informationincludes, for example, a part or the entirety of prediction parameterinformation.

In addition, circuitry 160 then binarizes the frequency transformcoefficient information included in the image information, according tobinarization formats different between when arithmetic encoding isapplied to the binary data string and when arithmetic encoding is notapplied to the binary data string (S412).

In addition, when arithmetic encoding is not applied to the binary datastring, circuitry 160 binarizes the data value included in the frequencytransform coefficient information according to the conversion tableselected from the plurality of tables including the first table and thesecond table. Here, the first table includes association with a datavalue indicating 0 as the number of non-zero coefficients, and thesecond table does not include any association with a data valueindicating 0 as the number of non-zero coefficients.

In this way, when arithmetic encoding is not applied, encoder 100 iscapable of assisting reduction in coding amount of the frequencytransform coefficient information, using the conversion table selectedfrom the plurality of tables including the second table which does notinclude any association with a data value indicating 0 as the number ofnon-zero coefficients.

[An Example of a Fourth Encoding Operation Performed by the Encoder]

In the example of a fourth encoding operation, a data value indicatingthe number of non-zero coefficients is binarized in the same manner asin the example of the third encoding operation illustrated in FIG. 32.Specifically, circuitry 160 binarizes the data value indicating thenumber of non-zero coefficients included in a current basic blockaccording to a conversion table in which a plurality of data values anda plurality of binary values are associated with each other, to encodeimage information including the data value (S601).

FIG. 34 is a flowchart indicating binarization processing in an exampleof a fourth encoding operation performed by encoder 100 according toEmbodiment 1. In other words, FIG. 34 indicates a specific example ofbinarization processing in FIG. 32.

Circuitry 160 selects a conversion table from a plurality of tablesaccording to the position of a current basic block in a currentfrequency transform block (S661). The current frequency transform blockis a frequency transform block including the current basic block. Theplurality of tables include two or more tables which differ from eachother in difference between a longest bit length and a shortest bitlength of a plurality of binary values associated with a plurality ofdata values. Circuitry 160 then binarizes the data value according tothe selected conversion table (S662).

In this way, encoder 100 is capable of selecting the conversion tablefor binarizing the data value indicating the number of non-zerocoefficients, according to the position of the current basic block. Thecharacteristics of the number of non-zero coefficients differ dependingon the position of the current basic block. Accordingly, encoder 100 iscapable of reflecting the characteristics of the number of non-zerocoefficients in the selection of the conversion table, using theposition of the current basic block.

Accordingly, encoder 100 is capable of appropriately selecting theconversion table, and assists reduction in coding amount of thefrequency transform coefficient information.

When a preceding basic block is present at the same frequency level asthe frequency level at the position of the current basic block,circuitry 160 may select the conversion table, according to the positionof the current basic block and the number of non-zero coefficientsincluded in the preceding basic block.

Here, the preceding basic block is a basic block located before thecurrent basic block in the predetermined scan order defined in adescending order of frequencies in the one or more basic blocks whichconstitute the current frequency transform block. In addition, thefrequency level at the position of the current basic block is afrequency level corresponding to the position of the current basicblock.

In this way, encoder 100 is capable of selecting the conversion tableaccording to the non-zero coefficients of the preceding basic blockwhich is estimated to have a similar number of non-zero coefficientswith respect to the number of non-zero coefficients of the current basicblock.

In addition, when the preceding basic block has the same frequency levelas the frequency level at the position of the current basic block andthe number of non-zero coefficients included in the preceding basicblock is a first number, circuitry 160 may select the first table as theconversion table. When the preceding basic block has the same frequencylevel as the frequency level at the position of the current basic blockand the number of non-zero coefficients included in the preceding basicblock is a second number, circuitry 160 may select the second table asthe conversion table.

Here, the second number is larger than the first number. In addition,the difference between the longest bit length and the shortest bitlength of a plurality of binary values in the second table is smallerthan the difference between the longest bit length and the shortest bitlength of a plurality of binary values in the first table. In otherwords, when the number of non-zero coefficients included in thepreceding basic block is large, circuitry 160 may select, as theconversion table, the table in which the difference between the longestbit length and the shortest bit length of a plurality of binary valuesis small.

In this way, when the number of non-zero coefficients of the currentbasic block is estimated to be large according to the number of non-zerocoefficients of the preceding basic block, encoder 100 is capable ofselecting the table in which the difference in bit length is small asthe conversion table, and assisting reduction in increase in codingamount.

In addition, for example, no preceding basic block may be present at thesame frequency level as the frequency level at the position of thecurrent basic block, and a specific basic block may be present at afrequency level higher than the frequency level at the position of thecurrent basic block. Here, the specific basic block is a basic blockincluding the non-zero coefficient first in the predetermined scanorder. In this case, circuitry 160 may select, as the conversion table,the table in which the difference between the longest bit length and theshortest bit length is smaller than a predetermined difference, from theplurality of tables.

In this way, when the number of non-zero coefficients is estimated to belarge according to the relationship between the current basic block andthe specific basic block, encoder 100 is capable of selecting the tablein which the difference in bit length is small as the conversion table,and assisting reduction in increase in coding amount. The predetermineddifference is not limited to a fixed value, and may be determinedrelatively, for example, similarly to the difference between the longestbit length and the shortest bit length in the table having the secondsmallest difference in bit length among the plurality of tables.

Specifically, in the above case, circuitry 160 may select, as theconversion table, the table in which the difference between the longestbit length and the shortest bit length is the smallest in the pluralityof tables. In this way, when the number of non-zero coefficients isestimated to be large according to the relationship between the currentbasic block and the specific basic block, encoder 100 is capable ofselecting the table in which the difference in bit length is small asthe conversion table, and assisting reduction in increase in codingamount.

In addition, for example, no preceding basic block may be present at thesame frequency level as the frequency level at the position of thecurrent basic block, and no specific basic block may be present at afrequency level higher than the frequency level at the position of thecurrent basic block. In this case, circuitry 160 may select theconversion table according to the number of non-zero coefficientsestimated to be the number of non-zero coefficients, based on aneighboring frequency transform block which is a frequency transformblock located around the current frequency transform block.

In this way, encoder 100 is capable of selecting the conversion tableusing the neighboring frequency transform block which is estimated tohave a similar number of non-zero coefficients with respect to thenumber of non-zero coefficients of the current basic block.

In addition, in the above case, circuitry 160 may select the first tablewhen the number of non-zero coefficients estimated based on theneighboring frequency transform block is the first number, and thesecond table when the number of non-zero coefficients estimated based onthe neighboring frequency transform block is the second number. Here,the second number is larger than the first number. In addition, thedifference between the longest bit length and the shortest bit length ofa plurality of binary values in the second table is smaller than thedifference between the longest bit length and the shortest bit length ofa plurality of binary values in the first table.

In other words, when the number of non-zero coefficients estimated basedon the neighboring frequency transform block is large, circuitry 160 mayselect, as the conversion table, the table in which the differencebetween the longest bit length and the shortest bit length of aplurality of binary values is small. In this way, when the number ofnon-zero coefficients of the current basic block is estimated to belarge according to the neighboring frequency transform block, encoder100 is capable of selecting the table in which the difference in bitlength is small as the conversion table, and assisting reduction inincrease in coding amount.

In addition, the neighboring frequency transform block may be afrequency transform block adjacent to the left of or above the currentfrequency transform block. In this way, encoder 100 is capable ofpredicting the number of non-zero coefficients at high accuracyaccording to the number of non-zero coefficients included in thefrequency transform block close to the current frequency transformblock.

Alternatively, the neighboring frequency transform block may be afrequency transform block which has been encoded immediately before thecurrent frequency transform block. This enables simple prediction of thenumber of non-zero coefficients and reduction in memory capacity forstoring information related to the number of non-zero coefficients.

Alternatively, the neighboring frequency transform block may be afrequency transform block which is located within a predetermined rangefrom the current frequency transform block and whose coding mode whichis one of an inter prediction mode and an intra prediction mode is thesame as that of the current frequency transform block. In this way,encoder 100 is capable of predicting the number of non-zero coefficientsat high accuracy according to the frequency transform block whosetendency of occurrence of non-zero coefficients is estimated to besimilar to that of the current frequency transform block.

In addition, the number of non-zero coefficients included in the currentbasic block may be estimated based on the number of non-zerocoefficients included in one of the one or more basic blocks included inthe neighboring frequency transform block. The one basic block is abasic block whose position relative to the neighboring frequencytransform block is equivalent to the position of the current basic blockrelative to the current frequency transform block.

In this way, encoder 100 is capable of selecting a conversion tableaccording to the basic block included in the one or more basic blocksand estimated to have approximately the same number of non-zerocoefficients as the number of non-zero coefficients of the current basicblock.

Alternatively, the number of non-zero coefficients estimated based onthe neighboring frequency transform block may be estimated based on thenumber of non-zero coefficients included in the entirety of theneighboring frequency transform block. In this way, the information isintegrated regardless of the sizes of frequency transform blocks. Thisenables simple prediction of the number of non-zero coefficients andreduction in memory capacity for storing information related to thenumber of non-zero coefficients.

In addition, for example, no preceding basic block may be present at thesame frequency level as the frequency level at the position of thecurrent basic block, and no specific basic block may be present at afrequency level higher than the frequency level at the position of thecurrent basic block. In this case, circuitry 160 may select a conversiontable according to whether the coding mode of the current basic block isthe inter prediction mode or the intra prediction mode.

In this way, encoder 100 is capable of selecting the conversion tableaccording to the coding mode which is the inter prediction mode or theintra prediction mode. The characteristics of the number of non-zerocoefficients are estimated to be different depending on the coding mode.Accordingly, encoder 100 is capable of reflecting the characteristics ofthe number of non-zero coefficients in the selection of the conversiontable, using the coding mode. Accordingly, encoder 100 is capable ofappropriately selecting the conversion table, and assisting reduction incoding amount of the frequency transform coefficient information.

In addition, in the above case, circuitry 160 may select the first tablewhen the coding mode is the inter prediction mode, and select the secondtable when the coding mode is the intra prediction mode. Here, thedifference between the longest bit length and the shortest bit length ofa plurality of binary values in the second table is smaller than thedifference between the longest bit length and the shortest bit length ofa plurality of binary values in the first table.

In other words, when the coding mode is the intra prediction mode,circuitry 160 may select, as the conversion table, the table having thesmall difference between the longest bit length and the shortest bitlength of the plurality of binary values. In this way, encoder 100 iscapable of selecting the table having the small difference in bit lengthas the conversion table when the coding mode is the intra predictionmode in which the prediction accuracy is low and the number of non-zerocoefficients is large, thereby being capable of assisting reduction inincrease in coding amount.

As described above, for example, no preceding basic block may be presentat the same frequency level as the frequency level at the position ofthe current basic block, and no specific basic block may be present at afrequency level higher than the frequency level at the position of thecurrent basic block. In this case, circuitry 160 may select a conversiontable according to a quantization parameter which is used to encode acurrent basic block.

In this way, encoder 100 is capable of selecting the conversion tableaccording to the quantization parameter which is used to encode thecurrent basic block. The characteristics of the number of non-zerocoefficients are estimated to be different depending on the quantizationparameter. Accordingly, encoder 100 is capable of reflecting thecharacteristics of the number of non-zero coefficients in the selectionof the conversion table, using the quantization parameter. Accordingly,encoder 100 is capable of appropriately selecting the conversion table,and assisting reduction in coding amount of the frequency transformcoefficient information.

In addition, in the above case, circuitry 160 may select the first tablewhen the quantization parameter is a first value, and select the secondtable when the quantization parameter is a second value. Here, thesecond value is smaller than the first value. In addition, thedifference between the longest bit length and the shortest bit length ofa plurality of binary values in the second table is smaller than thedifference between the longest bit length and the shortest bit length ofa plurality of binary values in the first table.

In other words, when the quantization parameter is small, circuitry 160may select, as the conversion table, the table having the smalldifference between the longest bit length and the shortest bit length ofthe plurality of binary values. In this way, encoder 100 is capable ofselecting the table having the small difference in bit length as theconversion table when the quantization parameter is small and thus thenumber of non-zero coefficients is large, thereby being capable ofassisting reduction in increase in coding amount.

In addition, circuitry 160 may encode image information and output abitstream in which the image information has been encoded, in the samemanner as in the example of a first encoding operation. For example,circuitry 160 binarizes image information as in FIG. 28 (S401).Circuitry 160 then switches whether or not to apply arithmetic encodingto the binary data string in which the image information has beenbinarized (S402).

When arithmetic encoding is applied to the binary data string (Yes inS402), circuitry 160 applies arithmetic encoding to the binary datastring, and outputs a bitstream including the binary data string towhich arithmetic encoding has been applied (S403). When arithmeticencoding is not applied to the binary data string (No in S402),circuitry 160 skips applying arithmetic encoding to the binary datastring, and outputs a bitstream including the binary data string towhich arithmetic encoding has not been applied (S404).

In addition, as indicated in FIG. 29, circuitry 160 binarizes otherinformation included in the image information, according to thebinarization format which is common between when arithmetic encoding isapplied to the binary data string and when arithmetic encoding is notapplied to the binary data string (S411). The other informationincludes, for example, a part or the entirety of prediction parameterinformation.

In addition, circuitry 160 then binarizes the frequency transformcoefficient information included in the image information, according tobinarization formats different between when arithmetic encoding isapplied to the binary data string and when arithmetic encoding is notapplied to the binary data string (S412).

In addition, when arithmetic encoding is not applied to the binary datastring, circuitry 160 binarizes the data value included in the frequencytransform coefficient information according to the conversion tableselected from the plurality of tables, according to the position of thecurrent basic block. In this way, when arithmetic encoding is notapplied, encoder 100 is capable of assisting reduction in coding amountof frequency transform coefficient information, using the conversiontable which is selected from the plurality of tables using the positionof the current basic block.

It is to be noted that the difference between a longest bit length and ashortest bit length more corresponds to the ratio of the bit length ofthe binary value associated with the data values each indicating thenumber of non-zero coefficients of a current basic block, as the numberof non-zero coefficients of the current basic block increases.Accordingly, the difference between the longest bit length and theshortest bit length may be replaced with the ratio of the bit length ofthe binary value associated with the data values each indicating thenumber of non-zero coefficients of the current basic block, as thenumber of non-zero coefficients of the current basic block increases.

For example, the ratio is 0 or larger. In the table having the ratio of0, the bit length of the binary value associated with the data valueseach indicating the number of non-zero coefficients of the current blockdoes not increase even when the number of non-zero coefficients of thecurrent basic block increases. Accordingly, the difference between alongest bit length and a shortest bit length may be replaced with theratio of the bit length of binary value associated with the data valueseach indicating the number of non-zero coefficients of a current block,as the number of non-zero coefficients of the current basic blockincreases.

[A Mounting Example of the Decoder]

FIG. 35 is a block diagram illustrating a mounting example of decoder200 according to Embodiment 1. Decoder 200 includes circuitry 260 andmemory 262. For example, a plurality of constituent elements of decoder200 illustrated in FIGS. 10 and 12 are mounted as circuitry 260 andmemory 262 illustrated in FIG. 35.

Circuitry 260 is circuitry for performing information processing andaccessible to memory 262. For example, circuitry 260 is an exclusive orgeneral electronic circuit for decoding image information. Circuitry 260may be a processor such as a CPU. Alternatively, circuitry 260 may be anassembly of a plurality of electronic circuits. In addition, forexample, circuitry 260 may take the roles of two or more of theconstituent elements other than the constituent elements for storinginformation among the plurality of constituent elements of decoder 200illustrated in FIGS. 10 and 12.

Memory 262 is a general or exclusive memory for storing information fordecoding image information by circuitry 260. Memory 262 may be anelectronic circuit, or may be connected to circuitry 260. Alternatively,memory 262 may be an assembly of a plurality of electronic circuits. Inaddition, memory 262 may be a magnetic disc, an optical disc, or thelike, or may be represented as storage, a recording medium, or the like.In addition, memory 262 may be non-volatile memory, or volatile memory.

For example, a bitstream corresponding to encoded image information orimage information corresponding to a decoded bitstream may be stored inmemory 262. In addition, a program that is executed by circuitry 260 todecode image information may be stored in memory 262.

In addition, for example, circuitry 260 may take the roles of two ormore of the constituent elements other than the constituent elements forstoring information among the plurality of constituent elements ofdecoder 200 illustrated in FIGS. 10 and 12. Specifically, memory 262 maytake the roles of block memory 210 and frame memory 214 illustrated inFIG. 10, or the role of intermediate buffer 240 illustrated in FIG. 12.

It is to be noted that, in decoder 200, not all the plurality ofconstituent elements illustrated in FIGS. 10, 12, etc. may be mounted,or not all the plurality of processes described above may be performed.Part of the plurality of constituent elements illustrated in FIGS. 10,12, etc. may be included in one or more other devices, and part of theplurality of processes described above may be performed by the one ormore other devices.

In decoder 200, part of the plurality of constituent elementsillustrated in FIG. 10 and FIG. 12, etc. may be mounted, and thefrequency transform coefficient information may be encoded appropriatelyby means of part of the above-described processes being executed.

[An Example of a First Decoding Operation Performed by the Decoder]

FIG. 36 is a flowchart indicating an example of a first decodingoperation performed by decoder 200 according to Embodiment 1. Forexample, circuitry 260 of decoder 200 illustrated in FIG. 35 obtains abitstream in which image information has been encoded and decodes theimage information, by performing the operation indicated in FIG. 36.

Specifically, circuitry 260 obtains the bitstream including the binarydata string in which the image information has been binarized (S701).For example, the image information includes frequency transformcoefficient information related to the frequency components of theimage, prediction parameter information related to prediction methodsfor the image, and so on. Circuitry 260 then switches whether or not toapply arithmetic decoding to the binary data string included in thebitstream (S702).

When arithmetic decoding is applied to the binary data string (Yes inS702), circuitry 260 decodes the image information by applyingarithmetic decoding to the binary data string and inverse binarizing thebinary data to which arithmetic decoding has been applied (S703).

When arithmetic decoding is applied to the binary data string (No inS702), circuitry 260 decodes the image information by skipping applyingarithmetic decoding to the binary data sting and inverse binarizing thebinary data string to which arithmetic decoding has not been applied(S704).

In this way, decoder 200 is capable of skipping arithmetic decoding.Accordingly, decoder 200 is capable of supporting reduction inprocessing delay generated by the arithmetic decoding.

FIG. 37 is a flowchart indicating inverse binarization processing in thefirst decoding operation performed by decoder 200 according toEmbodiment 1. In other words, FIG. 37 indicates a specific example ofinverse binarization processing (S703 and S704) in FIG. 36.

Circuitry 260 inverse binarizes a second portion of the binary datastring according to an inverse binarization format which is commonbetween when arithmetic decoding is applied to the binary data stringand when arithmetic decoding is not applied to the binary data string(S711). The second portion is different from a later-described firstportion of the binary data string. The second portion of the binary datastring is a portion in which the other information different fromfrequency transform coefficient information has been binarized. Theother information includes, for example, a part or the entirety ofprediction parameter information.

In addition, circuitry 260 inverse binarizes the first portion accordingto inverse binarization formats which are different between whenarithmetic decoding is applied to the binary data string and whenarithmetic decoding is not applied to the binary data string (S712). Thefirst portion of the binary data string is a portion in which thefrequency transform coefficient information has been binarized. Morespecifically, the first portion of the binary data string may be aportion in which information including the frequency transformcoefficient information has been binarized.

In this way, decoder 200 is capable of appropriately inverse binarizingthe first portion corresponding to the frequency transform coefficientinformation which significantly affects the total coding amount,according to whether or not to apply arithmetic decoding to the binarydata string. Accordingly, decoder 200 is capable of appropriatelydecoding the frequency transform coefficient information, thereby beingable to reduce increase in the total coding amount.

It is to be noted that the processing order of the inverse binarizationof the second portion in which the other information has been binarized(S711) and the inverse binarization of the first portion in which thefrequency transform coefficient information has been binarized (S712)may be inversed. In addition, for example, the prediction parameterinformation includes: information related to encoding modes; informationrelated to prediction directions in intra prediction; informationrelated to reference pictures in inter prediction; and informationrelated to motion vectors in inter prediction.

Circuitry 260 may inverse binarizes the second portion in which thesekinds of information included in the prediction parameter informationhave been binarized, according to the inverse binarization format whichis common between when arithmetic decoding is applied to the binary datastring and when arithmetic decoding is not applied to the binary datastring. Alternatively, circuitry 260 may binarize at least one of thesekinds of information, according to the binarization format which iscommon between when arithmetic encoding is applied to the binary datastring and when arithmetic encoding is not applied to the binary datastring.

In addition, circuitry 260 may inverse binarize only the first portionwhich is included in the binary data string and in which the frequencytransform coefficient information has been binarized, according to theinverse binarization formats different depending on whether or not toapply arithmetic decoding to the binary data string. Circuitry 260 maythen inverse binarize all the portion other than the first portion inwhich the frequency transform coefficient information in the binary datastring has been binarized in the binary data string, regardless ofwhether or not to apply arithmetic decoding to the binary data string.

In this way, decoder 200 is capable of inverse binarizing all theportion other than the first portion corresponding to the frequencytransform coefficient information, according to the common inversebinarization format. Accordingly, the processing is simplified.

FIG. 38 is a flowchart indicating inverse binarization processing of thefirst portion corresponding to the frequency transform coefficientinformation in the first decoding operation performed by decoder 200according to Embodiment 1. In other words, FIG. 38 indicates a specificexample of inverse binarization processing of the first portioncorresponding to the frequency transform coefficient information (S712)in FIG. 37.

When arithmetic decoding is applied to a binary data string (Yes inS721), circuitry 260 inverse binarizes the first portion in whichfrequency transform coefficient information has been binarized,according to a first inverse binarization format (S722). When arithmeticdecoding is not applied to a binary data string (No in S721), circuitry260 inverse binarizes the first portion in which frequency transformcoefficient information has been binarized, according to a secondinverse binarization format (S723).

Circuitry 260 then inverse binarizes the first portion in whichfrequency transform coefficient information has been binarized accordingto an inverse binarization format which generates a smaller number ofbits when arithmetic decoding is not applied to the binary data stringthan when arithmetic decoding is applied to the binary data string. Inthis way, decoder 200 is capable of assisting reduction in coding amountof the frequency transform coefficient information when arithmeticdecoding is not applied.

[An Example of a Second Decoding Operation Performed by the Decoder]

FIG. 39 is a flowchart indicating an example of a second decodingoperation performed by decoder 200 according to Embodiment 1. Forexample, circuitry 260 of decoder 200 illustrated in FIG. 35 decodesimage information by performing the operation indicated in FIG. 39.

Specifically, circuitry 260 decodes position information indicating theposition of a specific basic block (S801). The specific basic block is abasic block including a non-zero coefficient first in the scan order inthe one or more basic blocks which constitute the frequency transformblock including a plurality of frequency transform coefficients, as oneof the plurality of frequency transform coefficients.

Circuitry 260 decodes only block information indicating the plurality offrequency transform coefficients which constitute each of basic blockswhich are the specific basic block and the following basic block(s) inthe predetermined scan order out of the one or more basic blocks whichconstitute the frequency transform block (S802).

In this way, decoder 200 is capable of decoding the position informationand the block information as the frequency transform coefficientinformation. Since decoder 200 decodes the block information of each ofthe specific basic block and the following basic block(s) in thepredetermined scan order, decoder 200 is capable of assisting reductionin the coding amount of the frequency transform coefficient information.

It is to be noted that circuitry 260 may decode the position informationonly when the number of the one or more basic blocks which constitute afrequency transform block is two or more. In this way, when, forexample, the size of the frequency transform block and the size of eachbasic block is the same, decoder 200 is capable of assisting furtherreduction in coding amount of the frequency transform coefficientinformation.

In addition, circuitry 260 may decode position information and blockinformation only when a specific basic block is present in a frequencytransform block. In this way, when, for example, the frequency transformblock does not include any non-zero coefficient, decoder 200 is capableof assisting further reduction in coding amount of the frequencytransform coefficient information.

In addition, circuitry 260 may obtain a bitstream in which imageinformation has been encoded and decode the image information, in thesame manner as in the example of the first encoding operation. Forexample, as in FIG. 36, circuitry 260 obtains the bitstream includingthe binary data string in which the image information has been binarized(S701). Circuitry 260 then switches whether or not to apply arithmeticdecoding to the binary data string included in the bitstream (S702).

When arithmetic decoding is applied to the binary data string (Yes inS702), circuitry 260 decodes the image information by applyingarithmetic decoding to the binary data string and inverse binarizing thebinary data string to which arithmetic decoding has been applied (S703).When arithmetic decoding is not applied to the binary data string (No inS702), circuitry 260 decodes the image information by skipping applyingarithmetic decoding to the binary data sting and inverse binarizing thebinary data string to which arithmetic decoding has not been applied(S704).

In addition, as in FIG. 37, circuitry 260 inverse binarizes a secondportion according to an inverse binarization format which is commonbetween when arithmetic decoding is applied to the binary data stringand when arithmetic decoding is not applied to the binary data string(S711). The second portion of the binary data string is a portion inwhich the information other than the frequency transform coefficientinformation has been binarized. The other information includes, forexample, a part or the entirety of prediction parameter information.

In addition, circuitry 260 inverse binarizes the first portion accordingto inverse binarization formats which are different between whenarithmetic decoding is applied to the binary data string and whenarithmetic decoding is not applied to the binary data string (S712). Thefirst portion of the binary data string is a portion in which thefrequency transform coefficient information has been binarized.

In addition, when arithmetic decoding is not applied to the binary datastring, circuitry 260 decodes the position information and the blockinformation by inverse binarizing the first portion in which thefrequency transform coefficient information including the positioninformation and the block information. Here, the block information whichis decoded is the block information of the specific basic block and thefollowing basic block(s) in the predetermined scan order. In this way,decoder 200 is capable of assisting reduction in coding amount of thefrequency transform coefficient information when arithmetic decoding isnot applied.

[An Example of a Third Decoding Operation Performed by the Decoder]

FIG. 40 is a flowchart indicating an example of a third decodingoperation performed by decoder 200 according to Embodiment 1. Forexample, circuitry 260 of decoder 200 illustrated in FIG. 35 decodesimage information by performing the operation indicated in FIG. 40.

Specifically, circuitry 260 inverse binarizes the binary values obtainedby binarizing a plurality of data values each indicating the number ofnon-zero coefficients included in the current basic block, according toa conversion table in which the plurality of data values and a pluralityof binary values are associated with each other. Circuitry 260 thendecodes the image information including the data values (S901). Here,the current basic block is one of the one or more basic blocks whichconstitute the frequency transform block including the plurality offrequency transform coefficients.

In this way, decoder 200 is capable of appropriately decodingsignificant information which is used for efficient representation ofthe plurality of frequency transform coefficients which constitute thebasic block.

FIG. 41 is a flowchart indicating inverse binarization processing in theexample of the third decoding operation performed by decoder 200according to Embodiment 1. In other words, FIG. 41 indicates a specificexample of inverse binarization processing in FIG. 40.

Circuitry 260 selects a conversion table from a plurality of tablesincluding a first table which includes association with a data valueindicating 0 as the number of non-zero coefficients and a second tablewhich does not include any association with a data value indicating 0 asthe number of non-zero coefficients (S911). Circuitry 260 then binarizesthe binary values according to the selected conversion table (S912).

In this way, decoder 200 is capable of using the table having a reducedinformation amount as the conversion table for inverse binarization. Inthis way, decoder 200 is capable of assisting reduction in coding amountof the frequency transform coefficient information.

Circuitry 260 may inverse binarize only the binary values obtained bybinarizing the data values each indicating the number of non-zerocoefficients included in each of the specific basic block and thefollowing basic block(s) in the predetermined scan order out of the oneor more basic blocks which constitute the frequency transform block. Inother words, circuitry 260 may inverse binarize the binary valuesobtained by binarizing the data values each indicating the number ofnon-zero coefficients of each of the specific basic block and thefollowing basic block(s) in the predetermined scan order, as the binaryvalues obtained by binarizing the data values each indicating the numberof non-zero coefficients of a current basic block.

In this way, decoder 200 is capable of assisting reduction in codingamount of the frequency transform coefficient information. It is to benoted that the specific basic block is a basic block including anon-zero coefficient first in the scan order which is defined in adescending order of frequencies in the one or more basic blocks whichconstitute the frequency transform block including a plurality offrequency transform coefficients, as one of the plurality of frequencytransform coefficients.

In addition, circuitry 260 may inverse binarize the binary valuesobtained by binarizing the data values each indicating the number ofnon-zero coefficients of the current basic block only when a specificbasic block is included in the one or more basic blocks which constitutethe frequency transform block. When the frequency transform block andthe current basic block are the same, circuitry 260 may then select, asthe conversion table, the second table which does not include anyassociation with a data value indicating 0 as the number of non-zerocoefficients.

In this way, when, for example, the size of the frequency transformblock and the size of each basic block are the same, decoder 200 iscapable of assisting further reduction in coding amount of the frequencytransform coefficient information, using the second table which does notinclude any association with a data value indicating 0 as the number ofnon-zero coefficients.

In addition, when the current basic block is a specific basic block,circuitry 260 may select the second table which does not include anyassociation with a data value indicating 0 as the number of non-zerocoefficients, as the conversion table.

In this way, when, for example, the current basic block is a specificbasic block, decoder 200 is capable of assisting further reduction incoding amount of the frequency transform coefficient information, usingthe second table which does not include any association with a datavalue indicating 0 as the number of non-zero coefficients.

In addition, circuitry 260 may obtain a bitstream in which imageinformation has been encoded and decode the image information, in thesame manner as in the example of the first encoding operation. Forexample, as in FIG. 36, circuitry 260 obtains the bitstream includingthe binary data string in which the image information has been binarized(S701). Circuitry 260 then switches whether or not to apply arithmeticdecoding to the binary data string included in the bitstream (S702).

When arithmetic decoding is applied to the binary data string (Yes inS702), circuitry 260 decodes the image information by applyingarithmetic decoding to the binary data string and inverse binarizing thebinary data string to which arithmetic decoding has been applied (S703).When arithmetic decoding is not applied to the binary data string (No inS702), circuitry 260 decodes the image information by skipping applyingarithmetic decoding to the binary data sting and inverse binarizing thebinary data string to which arithmetic decoding has not been applied(S704).

In addition, as in FIG. 37, circuitry 260 inverse binarizes a secondportion according to an inverse binarization format which is commonbetween when arithmetic decoding is applied to the binary data stringand when arithmetic decoding is not applied to the binary data string(S711). The second portion of the binary data string is a portion inwhich the information other than the frequency transform coefficientinformation has been binarized. The other information includes, forexample, a part or the entirety of prediction parameter information.

In addition, circuitry 260 inverse binarizes the first portion accordingto inverse binarization formats which are different between whenarithmetic decoding is applied to the binary data string and whenarithmetic decoding is not applied to the binary data string (S712). Thefirst portion of the binary data string is a portion in which thefrequency transform coefficient information has been binarized.

In addition, when arithmetic decoding is not applied to the binary datastring, circuitry 260 inverse binarizes the binary values included inthe first portion in which frequency transform coefficient informationhas been binarized, according to the conversion table selected from theplurality of tables including the first table and the second table.Here, the first table includes association with a data value indicating0 as the number of non-zero coefficients, and the second table does notinclude any association with a data value indicating 0 as the number ofnon-zero coefficients.

In this way, when arithmetic decoding is not applied, decoder 200 iscapable of assisting reduction in coding amount of the frequencytransform coefficient information, using the conversion table selectedfrom the plurality of tables including the second table which does notinclude any association with a data value indicating 0 as the number ofnon-zero coefficients.

[An Example of a Fourth Decoding Operation Performed by the Decoder]

In the example of the fourth decoding operation, a data value indicatingthe number of non-zero coefficients is inverse binarized as in the caseof the example of the third decoding operation indicated in FIG. 40.Specifically, circuitry 260 inverse binarizes the binary values obtainedby binarizing a plurality of data values each indicating the number ofnon-zero coefficients included in the current basic block, according toa conversion table in which the plurality of data values and a pluralityof binary values are associated with each other (S901).

FIG. 42 is a flowchart indicating inverse binarization processing in theexample of the fourth decoding operation performed by decoder 200according to Embodiment 1. In other words, FIG. 42 indicates a specificexample of inverse binarization processing in FIG. 40.

Circuitry 260 selects a conversion table from a plurality of tablesaccording to the position of a current basic block in a currentfrequency transform block (S961). The current frequency transform blockis a frequency transform block including the current basic block. Theplurality of tables include two or more tables which differ from eachother in difference between a longest bit length and a shortest bitlength of a plurality of binary values associated with a plurality ofdata values. Circuitry 260 then inverse binarizes the binary valuesaccording to the selected conversion table (S962).

In this way, decoder 200 is capable of selecting the conversion tablefor inverse binarizing the data value indicating the number of non-zerocoefficients, according to the position of the current basic block. Thecharacteristics of the number of non-zero coefficients differ dependingon the position of the current basic block. Accordingly, decoder 200 iscapable of reflecting the characteristics of the number of non-zerocoefficients in the selection of the conversion table, using theposition of the current basic block.

Accordingly, decoder 200 is capable of appropriately selecting theconversion table, and assisting reduction in coding amount of thefrequency transform coefficient information.

When a preceding basic block has the same frequency level as thefrequency level at the position of the current basic block, circuitry260 may select the conversion table, according to the position of thecurrent basic block and the number of non-zero coefficients included inthe preceding basic block. Here, the preceding basic block is a basicblock located before the current basic block in a predetermined scanorder defined in a descending order of frequencies in the one or morebasic blocks which constitute the current frequency transform block. Inaddition, the frequency level at the position of the current basic blockis a frequency level corresponding to the position of the current basicblock.

In this way, decoder 200 is capable of selecting the conversion tableaccording to the non-zero coefficients of the preceding basic blockwhich is estimated to have a similar number of non-zero coefficientswith respect to the number of non-zero coefficients of the current basicblock.

In addition, when the preceding basic block has the same frequency levelas the frequency level at the position of the current basic block andthe number of non-zero coefficients included in the preceding basicblock is a first number, circuitry 260 may select the first table as theconversion table. When the preceding basic block has the same frequencylevel as the frequency level at the position of the current basic blockand the number of non-zero coefficients included in the preceding basicblock is a second number, circuitry 260 may select the second table asthe conversion table.

Here, the second number is larger than the first number. In addition,the difference between the longest bit length and the shortest bitlength of a plurality of binary values in the second table is smallerthan the difference between the longest bit length and the shortest bitlength of a plurality of binary values in the first table. In otherwords, when the number of non-zero coefficients included in thepreceding basic block is large, circuitry 260 may select, as theconversion table, the table in which the difference between the longestbit length and the shortest bit length of a plurality of binary valuesis small.

In this way, when the number of non-zero coefficients of the currentbasic block is estimated to be large according to the number of non-zerocoefficients of the preceding basic block, decoder 200 is capable ofselecting the table in which the difference in bit length is small asthe conversion table, and assisting reduction in increase in codingamount.

In addition, for example, no preceding basic block may be present at thesame frequency level as the frequency level at the position of thecurrent basic block, and a specific basic block may be present at afrequency level higher than the frequency level at the position of thecurrent basic block. Here, the specific basic block is a basic blockincluding the non-zero coefficient first in the predetermined scanorder. In this case, circuitry 260 may select, as the conversion table,the table in which the difference between the longest bit length and theshortest bit length is smaller than a predetermined difference from theplurality of tables.

In this way, when the number of non-zero coefficients is estimated to belarge according to the relationship between the current basic block andthe specific basic block, decoder 200 is capable of selecting the tablein which the difference in bit length is small as the conversion table,and assisting reduction in increase in coding amount. The predetermineddifference is not limited to a fixed value, and may be determinedrelatively, for example, similarly to the difference between the longestbit length and the shortest bit length in the table having the secondsmallest difference in bit length among the plurality of tables.

Specifically, in the above case, circuitry 260 may select, as theconversion table, the table in which the difference between the longestbit length and the shortest bit length is the smallest among theplurality of tables. In this way, when the number of non-zerocoefficients is estimated to be large according to the relationshipbetween the current basic block and the specific basic block, decoder200 is capable of selecting the table in which the difference in bitlength is small as the conversion table, and assisting reduction inincrease in coding amount.

In addition, for example, no preceding basic block may be present at thesame frequency level as the frequency level at the position of thecurrent basic block, and a specific basic block may be present at afrequency level higher than the frequency level at the position of thecurrent basic block. In this case, circuitry 260 may select theconversion table according to the number of non-zero coefficientsestimated to be the number of non-zero coefficients based on aneighboring frequency transform block which is a frequency transformblock located around the current frequency transform block.

In this way, decoder 200 is capable of selecting the conversion tableusing the neighboring frequency transform block which is estimated tohave a similar number of non-zero coefficients with respect to thenumber of non-zero coefficients of the current basic block.

In addition, in the above case, circuitry 260 may select the first tablewhen the number of non-zero coefficients estimated based on theneighboring frequency transform block is the first number, and thesecond table when the number of non-zero coefficients estimated based onthe neighboring frequency transform block is the second number. Here,the second number is larger than the first number. In addition, thedifference between the longest bit length and the shortest bit length ofa plurality of binary values in the second table is smaller than thedifference between the longest bit length and the shortest bit length ofa plurality of binary values in the first table.

In other words, when the number of non-zero coefficients estimated basedon the neighboring frequency transform block is large, circuitry 260 mayselect, as the conversion table, the table in which the differencebetween the longest bit length and the shortest bit length of aplurality of binary values is small. In this way, when the number ofnon-zero coefficients of the current basic block is estimated to belarge according to the neighboring frequency transform block, decoder200 is capable of selecting the table in which the difference in bitlength is small as the conversion table, and assisting reduction inincrease in coding amount.

In addition, the neighboring frequency transform block may be afrequency transform block adjacent to the left of or above the currentfrequency transform block. In this way, decoder 200 is capable ofpredicting the number of non-zero coefficients at high accuracyaccording to the number of non-zero coefficients included in thefrequency transform block close to the current frequency transformblock.

Alternatively, the neighboring frequency transform block may be afrequency transform block which has been decoded immediately before thecurrent frequency transform block. This enables simple prediction of thenumber of non-zero coefficients and reduction in memory capacity forstoring information related to the number of non-zero coefficients.

Alternatively, the neighboring frequency transform block may be afrequency transform block which is located within a predetermined rangefrom the current frequency transform block and whose coding mode whichis one of an inter prediction mode and an intra prediction mode is thesame as that of the current frequency transform block. In this way,decoder 200 is capable of predicting the number of non-zero coefficientsat high accuracy according to the frequency transform block whosetendency of occurrence of non-zero coefficients is estimated to besimilar to that of the current frequency transform block.

In addition, the number of non-zero coefficients included in the currentbasic block may be estimated based on the number of non-zerocoefficients included in one of the one or more basic blocks included inthe neighboring frequency transform block. The one basic block is abasic block whose position relative to the neighboring frequencytransform block is equivalent to the position of the current basic blockrelative to the current frequency transform block.

In this way, decoder 200 is capable of selecting a conversion tableaccording to the basic block estimated to have approximately the samenumber of non-zero coefficients as that of the current basic block, fromthe one or more basic blocks of the neighboring frequency transformblock.

Alternatively, the number of non-zero coefficients estimated based onthe neighboring frequency transform block may be estimated based on thenumber of non-zero coefficients included in the entirety of theneighboring frequency transform block. In this way, the information isintegrated regardless of the sizes of frequency transform blocks. Thisenables simple prediction of the number of non-zero coefficients andreduction in memory capacity for storing information related to thenumber of non-zero coefficients.

As described above, for example, no preceding basic block may be presentat the same frequency level as the frequency level at the position ofthe current basic block, and no specific basic block may be present at afrequency level higher than the frequency level at the position of thecurrent basic block. In this case, circuitry 260 may select a conversiontable according to whether the coding mode of the current basic block isthe inter prediction mode or the intra prediction mode.

In this way, decoder 200 is capable of selecting the conversion tableaccording to the coding mode which is the inter prediction mode or theintra prediction mode. The characteristics of the number of non-zerocoefficients are estimated to be different depending on the coding mode.Accordingly, decoder 200 is capable of reflecting the characteristics ofthe number of non-zero coefficients in the selection of the conversiontable, using the coding mode. Accordingly, decoder 200 is capable ofappropriately selecting the conversion table, and assisting reduction incoding amount of the frequency transform coefficient information.

In addition, in the above case, circuitry 260 may select the first tablewhen the coding mode is the inter prediction mode, and select the secondtable when the coding mode is the intra prediction mode. Here, thedifference between the longest bit length and the shortest bit length ofa plurality of binary values in the second table is smaller than thedifference between the longest bit length and the shortest bit length ofa plurality of binary values in the first table.

In other words, when the coding mode is the intra prediction mode,circuitry 260 may select, as the conversion table, the table having thesmall difference between the longest bit length and the shortest bitlength of the plurality of binary values. In this way, decoder 200 iscapable of selecting the table having the small difference in bit lengthas the conversion table when the coding mode is the intra predictionmode in which the prediction accuracy is low and the number of non-zerocoefficients is large, thereby assisting reduction in increase in codingamount.

As described above, for example, no preceding basic block may be presentat the same frequency level as the frequency level at the position ofthe current basic block, and no specific basic block may be present at afrequency level higher than the frequency level at the position of thecurrent basic block. In this case, circuitry 260 may select a conversiontable according to a quantization parameter which is used to decode acurrent basic block.

In this way, decoder 200 is capable of selecting the conversion tableaccording to the quantization parameter which is used to decode thecurrent basic block. The characteristics of the number of non-zerocoefficients are estimated to be different depending on the quantizationparameter. Accordingly, decoder 200 is capable of reflecting thecharacteristic of the number of non-zero coefficients in the selectionof the conversion table, using the quantization parameter. Accordingly,decoder 200 is capable of appropriately selecting the conversion table,and assisting reduction in coding amount of the frequency transformcoefficient information.

In addition, in the above case, circuitry 260 may select the first tablewhen the quantization parameter is a first value, and select the secondtable when the quantization parameter is a second value. Here, thesecond value is smaller than the first value. In addition, thedifference between the longest bit length and the shortest bit length ofa plurality of binary values in the second table is smaller than thedifference between the longest bit length and the shortest bit length ofa plurality of binary values in the first table.

In other words, when the quantization parameter is small, circuitry 260may select, as the conversion table, the table having the smalldifference between the longest bit length and the shortest bit length ofthe plurality of binary values. In this way, decoder 200 is capable ofselecting the table having the small difference in bit length as theconversion table when the quantization parameter is small and thus thenumber of non-zero coefficients is large, thereby assisting reduction inincrease in coding amount.

In addition, circuitry 260 may obtain a bitstream in which imageinformation has been encoded and decode the image information, in thesame manner as in the example of the first decoding operation. Forexample, as in FIG. 36, circuitry 260 obtains the bitstream includingthe binary data string in which the image information has been binarized(S701). Circuitry 260 then switches whether or not to apply arithmeticdecoding to the binary data string included in the bitstream (S702).

When arithmetic decoding is applied to the binary data string (Yes inS702), circuitry 260 decodes the image information by applyingarithmetic decoding to the binary data string and inverse binarizing thebinary data string to which arithmetic decoding has been applied (S703).When arithmetic decoding is not applied to the binary data string (No inS702), circuitry 260 decodes the image information by skipping applyingarithmetic decoding to the binary data sting and inverse binarizing thebinary data string to which arithmetic decoding has not been applied(S704).

In addition, as in FIG. 37, circuitry 260 inverse binarizes a secondportion according to an inverse binarization format which is commonbetween when arithmetic decoding is applied to the binary data stringand when arithmetic decoding is not applied to the binary data string(S711). The second portion of the binary data string is a portion inwhich the information other than the frequency transform coefficientinformation has been binarized. The other information includes, forexample, a part or the entirety of prediction parameter information.

In addition, circuitry 260 inverse binarizes the first portion accordingto inverse binarization formats which are different between whenarithmetic decoding is applied to the binary data string and whenarithmetic decoding is not applied to the binary data string (S712). Thefirst portion of the binary data string is a portion in which thefrequency transform coefficient information included in the binary datastring has been binarized.

In addition, when arithmetic decoding is not applied to the binary datastring, circuitry 260 inverse binarizes the binary values included inthe first portion in which the frequency transform coefficients havebeen binarized, according to the conversion table selected from theplurality of tables according to the position of the current basicblock. In this way, when arithmetic decoding is not applied, decoder 200is capable of assisting reduction in coding amount of frequencytransform coefficient information, using the conversion table which isselected from the plurality of tables according to the position of thecurrent basic block.

It is to be noted that the difference between a longest bit length and ashortest bit length more corresponds to the ratio of the bit length ofthe binary value associated with the data values each indicating thenumber of non-zero coefficients of a current basic block, as the numberof non-zero coefficients of the current basic block increases.Accordingly, the difference between a longest bit length and a shortestbit length may be replaced with the ratio of the bit length of thebinary value associated with the data values each indicating the numberof non-zero coefficients of the current basic block, as the number ofnon-zero coefficients of the current basic block increases.

For example, the ratio is 0 or larger. In the table having the ratio of0, the bit length of the binary value associated with the data valueseach indicating the number of non-zero coefficients of the current blockdoes not increase even when the number of non-zero coefficients of thecurrent basic block increases. Accordingly, the difference between alongest bit length and a shortest bit length may be replaced with theratio of the bit length of binary value associated with the data valueseach indicating the number of non-zero coefficients of the current basicblock, as the number of non-zero coefficients of the current basic blockincreases.

[Supplements]

Encoder 100 and decoder 200 can be used as an image encoder and an imagedecoder, respectively. Alternatively, encoder 100 and decoder 200 can beused as an entropy encoder and an entropy decoder, respectively. Inother words, encoder 100 and decoder 200 may correspond only to entropyencoder 110 and entropy decoder 202, respectively.

In addition, in each of the above embodiments, each of the constituentelements may be configured as exclusive hardware or may be implementedby executing a software program suitable for the constituent element.Each constituent element may be implemented by means of a programexecuting unit such as a CPU and a processor reading and executing asoftware program stored in a recording medium that is a hard disc, asemiconductor memory, or the like.

More specifically, each of encoder 100 and decoder 200 may includeprocessing circuitry and storage which is electrically connected to theprocessing circuitry and accessible from the processing circuitry. Forexample, the processing circuitry corresponds to circuitry 160 or 260,and the storage corresponds to memory 162 or 262.

The processing circuitry includes at least one of the exclusive hardwareand the program executing unit, and executes the processing using thestorage. In addition, when the processing circuitry includes the programexecuting unit, the storage stores a software program which is executedby the program executing unit.

Here, the software for implementing encoder 100, decoder 200, or thelike according to this embodiment includes programs as indicated below.

The program is a program causing a computer to execute an encodingmethod for encoding image information and outputting a bitstream inwhich the image information has been encoded, the encoding methodincluding: binarizing the image information; switching whether or not toapply arithmetic encoding to a binary data string in which the imageinformation has been binarized; when arithmetic encoding is applied tothe binary data string, applying arithmetic encoding to the binary datastring, and outputting the bitstream which includes the binary datastring to which arithmetic encoding has been applied; when arithmeticencoding is not applied to the binary data string, skipping applyingarithmetic encoding to the binary data string, and outputting thebitstream which includes the binary data string to which arithmeticencoding has not been applied; in the binarizing of the imageinformation, binarizing frequency transform coefficient informationwhich is related to frequency components of an image and included in theimage information, according to different binarization formats betweenwhen arithmetic encoding is applied to the binary data string and whenarithmetic encoding is not applied to the binary data string; and in thebinarizing of the image information, binarizing a part or an entirety ofprediction parameter information which is related to prediction methodsof the image and included in the image information, according to acommon binarization format between when arithmetic encoding is appliedto the binary data string and when arithmetic encoding is not applied tothe binary data string.

Alternatively, the program is a program causing a computer to execute adecoding method for obtaining a bitstream in which image information hasbeen encoded and decoding the image information, the decoding methodincluding: obtaining the bitstream which includes a binary data stringin which the image information has been binarized; switching whether ornot to apply arithmetic decoding to the binary data string included inthe bitstream; when arithmetic decoding is applied to the binary datastring, applying arithmetic decoding to the binary data string, andinverse binarizing the binary data string to which arithmetic decodinghas been applied, to decode the image information; when arithmeticdecoding is not applied to the binary data string, skipping applyingarithmetic decoding to the binary data string, and inverse binarizingthe binary data string to which arithmetic decoding has not beenapplied, to decode the image information; in the inverse binarizing ofthe binary data string, inverse binarizing a first portion which isincluded in the binary data string and in which frequency transformcoefficient information related to frequency components of an image hasbeen binarized, according to different inverse binarization formatsbetween when arithmetic decoding is applied to the binary data stringand when arithmetic decoding is not applied to the binary data string;and in the inverse binarizing of the binary data string, inversebinarizing a second portion which is included in the binary data stringand in which a part or an entirety of prediction parameter informationrelated to prediction methods of an image has been binarized, accordingto a common inverse binarization format between when arithmetic decodingis applied to the binary data string and when arithmetic decoding is notapplied to the binary data string.

Alternatively, the program is a program causing a computer to execute anencoding method for encoding image information, the encoding methodincluding: encoding position information indicating a position of aspecific basic block which is a basic block including a non-zerocoefficient first in a predetermined scan order defined in a descendingorder of frequencies of one or more basic blocks included in a frequencytransform block composed of a plurality of frequency transformcoefficients; and encoding only block information indicating a pluralityof frequency transform coefficients of each of the specific basic blockand a following basic block in the predetermined scan order.

Alternatively, the program is a program causing a computer to execute adecoding method for decoding image information, the decoding methodincluding: decoding position information indicating a position of aspecific basic block which is a basic block including a non-zerocoefficient first in a predetermined scan order defined in a descendingorder of frequencies of one or more basic blocks included in a frequencytransform block composed of a plurality of frequency transformcoefficients; and decoding only block information indicating a pluralityof frequency transform coefficients of each of the specific basic blockand a following basic block in the predetermined scan order.

Alternatively, the program is a program causing a computer to execute anencoding method for encoding image information, the encoding methodincluding: binarizing a data value indicating the number of non-zerocoefficients included in a current basic block which is one of one ormore basic blocks in a frequency transform block composed of a pluralityof frequency transform coefficients, according to a conversion table inwhich a plurality of data values and a plurality of binary values areassociated with each other, to encode the image information whichincludes the data value; and in the binarizing of the data value,selecting the conversion table from a plurality of tables including afirst table which includes association with a data value indicating 0 asthe number of non-zero coefficients and a second table which does notinclude association with a data value indicating 0 as the number ofnon-zero coefficients, and binarizing the data value according to theconversion table selected.

Alternatively, the program is a program causing a computer to execute adecoding method for decoding image information, the decoding methodincluding: inverse binarizing a binary value which has been obtained bybinarizing a data value according to a conversion table in which aplurality of data values and a plurality of binary values are associatedwith each other, to decode the image information which includes the datavalue, the data value indicating the number of non-zero coefficientsincluded in a current basic block which is one of one or more basicblocks in a frequency transform block composed of a plurality offrequency transform coefficients; and in the inverse binarizing of thedata value, selecting the conversion table from a plurality of tablesincluding a first table which includes association with a data valueindicating 0 as the number of non-zero coefficients and a second tablewhich does not include association with a data value indicating 0 as thenumber of non-zero coefficients, and inverse binarizing the binary valueaccording to the conversion table selected.

Alternatively, the program is a program causing a computer to execute anencoding method for encoding image information, the encoding methodincluding: binarizing a data value indicating the number of non-zerocoefficients included in a current basic block which is one of one ormore basic blocks in a frequency transform block composed of a pluralityof frequency transform coefficients, according to a conversion table inwhich a plurality of data values and a plurality of binary values areassociated with each other, to encode the image information whichincludes the data value; and in the binarizing of the data value,selecting the conversion table from a plurality of tables including twoor more tables which differ from each other in difference between alongest bit length and a shortest bit length of a plurality of binaryvalues associated with the plurality of data values, according to aposition of the current basic block in the current frequency transformblock which is the frequency transform block including the current basicblock, and binarizing the data value.

Alternatively, the program is a program causing a computer to execute adecoding method for decoding image information, the decoding methodincluding: inverse binarizing a binary value which has been obtained bybinarizing a data value, according to a conversion table in which aplurality of data values and a plurality of binary values are associatedwith each other, to decode the image information which includes the datavalue, the data value indicating the number of non-zero coefficientsincluded in a current basic block which is one of one or more basicblocks in a frequency transform block composed of a plurality offrequency transform coefficients; and in the inverse binarizing of thebinary value, selecting the conversion table from a plurality of tablesincluding two or more tables which differ from each other in differencebetween a longest bit length and a shortest bit length of a plurality ofbinary values associated with the plurality of data values, according toa position of the current basic block in the current frequency transformblock which is the frequency transform block including the current basicblock, and inverse binarizing the binary value according to theconversion table selected.

In addition, each of the constituent elements may be the circuitry asdescribed above. The circuitry may be configured as a single circuit asa whole, or as separate circuits. In addition, each constituent elementmay be implemented as a general processor, or an exclusive processor.

In addition, the processing which is executed by a particular one of theconstituent elements may be executed by another one of the constituentelements. In addition, the execution order of the processes may bemodified, or two or more of the processes may be executed in parallel.In addition, an encoder and decoder may include encoder 100 and decoder200.

The ordinal numbers such as first, second, etc. used for explanation maybe arbitrarily replaced. In addition, an ordinal number may be newlyadded to a given one of the constituent elements, or the like, or theordinal number of a given one of the constituent elements, or the likemay be removed.

Encoder 100 and decoder 200 according to one or more aspects have beendescribed above based on the embodiments, the present disclosure is notlimited to these embodiments. The one or more aspects of the presentdisclosure may encompass embodiments obtainable by adding, to theembodiments, various kinds of modifications that a person skilled in theart would arrive at and embodiments configurable by combiningconstituent elements in different embodiments within the scope of thepresent disclosure.

Embodiment 2

As described in each of the above embodiments, each functional block cantypically be realized as an MPU and memory, for example. Moreover,processes performed by each of the functional blocks are typicallyrealized by a program execution unit, such as a processor, reading andexecuting software (a program) recorded on a recording medium such asROM. The software may be distributed via, for example, downloading, andmay be recorded on a recording medium such as semiconductor memory anddistributed. Note that each functional block can, of course, also berealized as hardware (dedicated circuit).

Moreover, the processing described in each of the embodiments may berealized via integrated processing using a single apparatus (system),and, alternatively, may be realized via decentralized processing using aplurality of apparatuses. Moreover, the processor that executes theabove-described program may be a single processor or a plurality ofprocessors. In other words, integrated processing may be performed, and,alternatively, decentralized processing may be performed.

Embodiments of the present disclosure are not limited to the aboveexemplary embodiments; various modifications may be made to theexemplary embodiments, the results of which are also included within thescope of the embodiments of the present disclosure.

Next, application examples of the moving picture encoding method (imageencoding method) and the moving picture decoding method (image decodingmethod) described in each of the above embodiments and a system thatemploys the same will be described. The system is characterized asincluding an image encoder that employs the image encoding method, animage decoder that employs the image decoding method, and an imageencoding/decoder that includes both the image encoder and the imagedecoder. Other configurations included in the system may be modified ona case-by-case basis.

Usage Examples

FIG. 29 illustrates an overall configuration of content providing systemex100 for implementing a content distribution service. The area in whichthe communication service is provided is divided into cells of desiredsizes, and base stations ex106, ex107, ex108, ex109, and ex110, whichare fixed wireless stations, are located in respective cells.

In content providing system ex100, devices including computer ex111,gaming device ex112, camera ex113, home appliance ex114, and smartphoneex115 are connected to internet ex101 via internet service providerex102 or communications network ex104 and base stations ex106 throughex110. Content providing system ex100 may combine and connect anycombination of the above elements. The devices may be directly orindirectly connected together via a telephone network or near fieldcommunication rather than via base stations ex106 through ex110, whichare fixed wireless stations. Moreover, streaming server ex103 isconnected to devices including computer ex111, gaming device ex112,camera ex113, home appliance ex114, and smartphone ex115 via, forexample, internet ex101. Streaming server ex103 is also connected to,for example, a terminal in a hotspot in airplane ex117 via satelliteex116.

Note that instead of base stations ex106 through ex110, wireless accesspoints or hotspots may be used. Streaming server ex103 may be connectedto communications network ex104 directly instead of via internet ex101or internet service provider ex102, and may be connected to airplaneex117 directly instead of via satellite ex116.

Camera ex113 is a device capable of capturing still images and video,such as a digital camera. Smartphone ex115 is a smartphone device,cellular phone, or personal handyphone system (PHS) phone that canoperate under the mobile communications system standards of the typical2G, 3G, 3.9G, and 4G systems, as well as the next-generation 5G system.

Home appliance ex118 is, for example, a refrigerator or a deviceincluded in a home fuel cell cogeneration system.

In content providing system ex100, a terminal including an image and/orvideo capturing function is capable of, for example, live streaming byconnecting to streaming server ex103 via, for example, base stationex106. When live streaming, a terminal (e.g., computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, orairplane ex117) performs the encoding processing described in the aboveembodiments on still-image or video content captured by a user via theterminal, multiplexes video data obtained via the encoding and audiodata obtained by encoding audio corresponding to the video, andtransmits the obtained data to streaming server ex103. In other words,the terminal functions as the image encoder according to one aspect ofthe present disclosure.

Streaming server ex103 streams transmitted content data to clients thatrequest the stream. Client examples include computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, andterminals inside airplane ex117, which are capable of decoding theabove-described encoded data. Devices that receive the streamed datadecode and reproduce the received data. In other words, the devices eachfunction as the image decoder according to one aspect of the presentdisclosure.

[Decentralized Processing]

Streaming server ex103 may be realized as a plurality of servers orcomputers between which tasks such as the processing, recording, andstreaming of data are divided. For example, streaming server ex103 maybe realized as a content delivery network (CDN) that streams content viaa network connecting multiple edge servers located throughout the world.In a CDN, an edge server physically near the client is dynamicallyassigned to the client. Content is cached and streamed to the edgeserver to reduce load times. In the event of, for example, some kind ofan error or a change in connectivity due to, for example, a spike intraffic, it is possible to stream data stably at high speeds since it ispossible to avoid affected parts of the network by, for example,dividing the processing between a plurality of edge servers or switchingthe streaming duties to a different edge server, and continuingstreaming.

Decentralization is not limited to just the division of processing forstreaming; the encoding of the captured data may be divided between andperformed by the terminals, on the server side, or both. In one example,in typical encoding, the processing is performed in two loops. The firstloop is for detecting how complicated the image is on a frame-by-frameor scene-by-scene basis, or detecting the encoding load. The second loopis for processing that maintains image quality and improves encodingefficiency. For example, it is possible to reduce the processing load ofthe terminals and improve the quality and encoding efficiency of thecontent by having the terminals perform the first loop of the encodingand having the server side that received the content perform the secondloop of the encoding. In such a case, upon receipt of a decodingrequest, it is possible for the encoded data resulting from the firstloop performed by one terminal to be received and reproduced on anotherterminal in approximately real time. This makes it possible to realizesmooth, real-time streaming.

In another example, camera ex113 or the like extracts a feature amountfrom an image, compresses data related to the feature amount asmetadata, and transmits the compressed metadata to a server. Forexample, the server determines the significance of an object based onthe feature amount and changes the quantization accuracy accordingly toperform compression suitable for the meaning of the image. Featureamount data is particularly effective in improving the precision andefficiency of motion vector prediction during the second compressionpass performed by the server. Moreover, encoding that has a relativelylow processing load, such as variable length coding (VLC), may behandled by the terminal, and encoding that has a relatively highprocessing load, such as context-adaptive binary arithmetic coding(CABAC), may be handled by the server.

In yet another example, there are instances in which a plurality ofvideos of approximately the same scene are captured by a plurality ofterminals in, for example, a stadium, shopping mall, or factory. In sucha case, for example, the encoding may be decentralized by dividingprocessing tasks between the plurality of terminals that captured thevideos and, if necessary, other terminals that did not capture thevideos and the server, on a per-unit basis. The units may be, forexample, groups of pictures (GOP), pictures, or tiles resulting fromdividing a picture. This makes it possible to reduce load times andachieve streaming that is closer to real-time.

Moreover, since the videos are of approximately the same scene,management and/or instruction may be carried out by the server so thatthe videos captured by the terminals can be cross-referenced. Moreover,the server may receive encoded data from the terminals, change referencerelationship between items of data or correct or replace picturesthemselves, and then perform the encoding. This makes it possible togenerate a stream with increased quality and efficiency for theindividual items of data.

Moreover, the server may stream video data after performing transcodingto convert the encoding format of the video data. For example, theserver may convert the encoding format from MPEG to VP, and may convertH.264 to H.265.

In this way, encoding can be performed by a terminal or one or moreservers. Accordingly, although the device that performs the encoding isreferred to as a “server” or “terminal” in the following description,some or all of the processes performed by the server may be performed bythe terminal, and likewise some or all of the processes performed by theterminal may be performed by the server. This also applies to decodingprocesses.

[3D, Multi-Angle]

In recent years, usage of images or videos combined from images orvideos of different scenes concurrently captured or the same scenecaptured from different angles by a plurality of terminals such ascamera ex113 and/or smartphone ex115 has increased. Videos captured bythe terminals are combined based on, for example, theseparately-obtained relative positional relationship between theterminals, or regions in a video having matching feature points.

In addition to the encoding of two-dimensional moving pictures, theserver may encode a still image based on scene analysis of a movingpicture either automatically or at a point in time specified by theuser, and transmit the encoded still image to a reception terminal.Furthermore, when the server can obtain the relative positionalrelationship between the video capturing terminals, in addition totwo-dimensional moving pictures, the server can generatethree-dimensional geometry of a scene based on video of the same scenecaptured from different angles. Note that the server may separatelyencode three-dimensional data generated from, for example, a pointcloud, and may, based on a result of recognizing or tracking a person orobject using three-dimensional data, select or reconstruct and generatea video to be transmitted to a reception terminal from videos capturedby a plurality of terminals.

This allows the user to enjoy a scene by freely selecting videoscorresponding to the video capturing terminals, and allows the user toenjoy the content obtained by extracting, from three-dimensional datareconstructed from a plurality of images or videos, a video from aselected viewpoint. Furthermore, similar to with video, sound may berecorded from relatively different angles, and the server may multiplex,with the video, audio from a specific angle or space in accordance withthe video, and transmit the result.

In recent years, content that is a composite of the real world and avirtual world, such as virtual reality (VR) and augmented reality (AR)content, has also become popular. In the case of VR images, the servermay create images from the viewpoints of both the left and right eyesand perform encoding that tolerates reference between the two viewpointimages, such as multi-view coding (MVC), and, alternatively, may encodethe images as separate streams without referencing. When the images aredecoded as separate streams, the streams may be synchronized whenreproduced so as to recreate a virtual three-dimensional space inaccordance with the viewpoint of the user.

In the case of AR images, the server superimposes virtual objectinformation existing in a virtual space onto camera informationrepresenting a real-world space, based on a three-dimensional positionor movement from the perspective of the user. The decoder may obtain orstore virtual object information and three-dimensional data, generatetwo-dimensional images based on movement from the perspective of theuser, and then generate superimposed data by seamlessly connecting theimages. Alternatively, the decoder may transmit, to the server, motionfrom the perspective of the user in addition to a request for virtualobject information, and the server may generate superimposed data basedon three-dimensional data stored in the server in accordance with thereceived motion, and encode and stream the generated superimposed datato the decoder. Note that superimposed data includes, in addition to RGBvalues, an a value indicating transparency, and the server sets the avalue for sections other than the object generated fromthree-dimensional data to, for example, 0, and may perform the encodingwhile those sections are transparent. Alternatively, the server may setthe background to a predetermined RGB value, such as a chroma key, andgenerate data in which areas other than the object are set as thebackground.

Decoding of similarly streamed data may be performed by the client(i.e., the terminals), on the server side, or divided therebetween. Inone example, one terminal may transmit a reception request to a server,the requested content may be received and decoded by another terminal,and a decoded signal may be transmitted to a device having a display. Itis possible to reproduce high image quality data by decentralizingprocessing and appropriately selecting content regardless of theprocessing ability of the communications terminal itself. In yet anotherexample, while a TV, for example, is receiving image data that is largein size, a region of a picture, such as a tile obtained by dividing thepicture, may be decoded and displayed on a personal terminal orterminals of a viewer or viewers of the TV. This makes it possible forthe viewers to share a big-picture view as well as for each viewer tocheck his or her assigned area or inspect a region in further detail upclose.

In the future, both indoors and outdoors, in situations in which aplurality of wireless connections are possible over near, mid, and fardistances, it is expected to be able to seamlessly receive content evenwhen switching to data appropriate for the current connection, using astreaming system standard such as MPEG-DASH. With this, the user canswitch between data in real time while freely selecting a decoder ordisplay apparatus including not only his or her own terminal, but also,for example, displays disposed indoors or outdoors. Moreover, based on,for example, information on the position of the user, decoding can beperformed while switching which terminal handles decoding and whichterminal handles the displaying of content. This makes it possible to,while in route to a destination, display, on the wall of a nearbybuilding in which a device capable of displaying content is embedded oron part of the ground, map information while on the move. Moreover, itis also possible to switch the bit rate of the received data based onthe accessibility to the encoded data on a network, such as when encodeddata is cached on a server quickly accessible from the receptionterminal or when encoded data is copied to an edge server in a contentdelivery service.

[Scalable Encoding]

The switching of content will be described with reference to a scalablestream, illustrated in FIG. 44, that is compression coded viaimplementation of the moving picture encoding method described in theabove embodiments. The server may have a configuration in which contentis switched while making use of the temporal and/or spatial scalabilityof a stream, which is achieved by division into and encoding of layers,as illustrated in FIG. 44. Note that there may be a plurality ofindividual streams that are of the same content but different quality.In other words, by determining which layer to decode up to based oninternal factors, such as the processing ability on the decoder side,and external factors, such as communication bandwidth, the decoder sidecan freely switch between low resolution content and high resolutioncontent while decoding. For example, in a case in which the user wantsto continue watching, at home on a device such as a TV connected to theinternet, a video that he or she had been previously watching onsmartphone ex115 while on the move, the device can simply decode thesame stream up to a different layer, which reduces server side load.

Furthermore, in addition to the configuration described above in whichscalability is achieved as a result of the pictures being encoded perlayer and the enhancement layer is above the base layer, the enhancementlayer may include metadata based on, for example, statisticalinformation on the image, and the decoder side may generate high imagequality content by performing super-resolution imaging on a picture inthe base layer based on the metadata. Super-resolution imaging may beimproving the SN ratio while maintaining resolution and/or increasingresolution. Metadata includes information for identifying a linear or anon-linear filter coefficient used in super-resolution processing, orinformation identifying a parameter value in filter processing, machinelearning, or least squares method used in super-resolution processing.

Alternatively, a configuration in which a picture is divided into, forexample, tiles in accordance with the meaning of, for example, an objectin the image, and on the decoder side, only a partial region is decodedby selecting a tile to decode, is also acceptable. Moreover, by storingan attribute about the object (person, car, ball, etc.) and a positionof the object in the video (coordinates in identical images) asmetadata, the decoder side can identify the position of a desired objectbased on the metadata and determine which tile or tiles include thatobject. For example, as illustrated in FIG. 45, metadata is stored usinga data storage structure different from pixel data such as an SEImessage in HEVC. This metadata indicates, for example, the position,size, or color of the main object.

Moreover, metadata may be stored in units of a plurality of pictures,such as stream, sequence, or random access units. With this, the decoderside can obtain, for example, the time at which a specific personappears in the video, and by fitting that with picture unit information,can identify a picture in which the object is present and the positionof the object in the picture.

[Web Page Optimization]

FIG. 46 illustrates an example of a display screen of a web page on, forexample, computer ex111. FIG. 47 illustrates an example of a displayscreen of a web page on, for example, smartphone ex115. As illustratedin FIG. 46 and FIG. 47, a web page may include a plurality of imagelinks which are links to image content, and the appearance of the webpage differs depending on the device used to view the web page. When aplurality of image links are viewable on the screen, until the userexplicitly selects an image link, or until the image link is in theapproximate center of the screen or the entire image link fits in thescreen, the display apparatus (decoder) displays, as the image links,still images included in the content or I pictures, displays video suchas an animated gif using a plurality of still images or I pictures, forexample, or receives only the base layer and decodes and displays thevideo.

When an image link is selected by the user, the display apparatusdecodes giving the highest priority to the base layer. Note that ifthere is information in the HTML code of the web page indicating thatthe content is scalable, the display apparatus may decode up to theenhancement layer. Moreover, in order to guarantee real timereproduction, before a selection is made or when the bandwidth isseverely limited, the display apparatus can reduce delay between thepoint in time at which the leading picture is decoded and the point intime at which the decoded picture is displayed (that is, the delaybetween the start of the decoding of the content to the displaying ofthe content) by decoding and displaying only forward reference pictures(I picture, P picture, forward reference B picture). Moreover, thedisplay apparatus may purposely ignore the reference relationshipbetween pictures and coarsely decode all B and P pictures as forwardreference pictures, and then perform normal decoding as the number ofpictures received over time increases.

[Autonomous Driving]

When transmitting and receiving still image or video data such two- orthree-dimensional map information for autonomous driving or assisteddriving of an automobile, the reception terminal may receive, inaddition to image data belonging to one or more layers, information on,for example, the weather or road construction as metadata, and associatethe metadata with the image data upon decoding. Note that metadata maybe assigned per layer and, alternatively, may simply be multiplexed withthe image data.

In such a case, since the automobile, drone, airplane, etc., includingthe reception terminal is mobile, the reception terminal can seamlesslyreceive and decode while switching between base stations among basestations ex106 through ex110 by transmitting information indicating theposition of the reception terminal upon reception request. Moreover, inaccordance with the selection made by the user, the situation of theuser, or the bandwidth of the connection, the reception terminal candynamically select to what extent the metadata is received or to whatextent the map information, for example, is updated.

With this, in content providing system ex100, the client can receive,decode, and reproduce, in real time, encoded information transmitted bythe user.

[Streaming of Individual Content]

In content providing system ex100, in addition to high image quality,long content distributed by a video distribution entity, unicast ormulticast streaming of low image quality, short content from anindividual is also possible. Moreover, such content from individuals islikely to further increase in popularity. The server may first performediting processing on the content before the encoding processing inorder to refine the individual content. This may be achieved with, forexample, the following configuration.

In real-time while capturing video or image content or after the contenthas been captured and accumulated, the server performs recognitionprocessing based on the raw or encoded data, such as capture errorprocessing, scene search processing, meaning analysis, and/or objectdetection processing. Then, based on the result of the recognitionprocessing, the server either when prompted or automatically—edits thecontent, examples of which include: correction such as focus and/ormotion blur correction; removing low-priority scenes such as scenes thatare low in brightness compared to other pictures or out of focus; objectedge adjustment; and color tone adjustment. The server encodes theedited data based on the result of the editing. It is known thatexcessively long videos tend to receive fewer views. Accordingly, inorder to keep the content within a specific length that scales with thelength of the original video, the server may, in addition to thelow-priority scenes described above, automatically clip out scenes withlow movement based on an image processing result. Alternatively, theserver may generate and encode a video digest based on a result of ananalysis of the meaning of a scene.

Note that there are instances in which individual content may includecontent that infringes a copyright, moral right, portrait rights, etc.Such an instance may lead to an unfavorable situation for the creator,such as when content is shared beyond the scope intended by the creator.Accordingly, before encoding, the server may, for example, edit imagesso as to blur faces of people in the periphery of the screen or blur theinside of a house, for example. Moreover, the server may be configuredto recognize the faces of people other than a registered person inimages to be encoded, and when such faces appear in an image, forexample, apply a mosaic filter to the face of the person. Alternatively,as pre- or post-processing for encoding, the user may specify, forcopyright reasons, a region of an image including a person or a regionof the background be processed, and the server may process the specifiedregion by, for example, replacing the region with a different image orblurring the region. If the region includes a person, the person may betracked in the moving picture the head region may be replaced withanother image as the person moves.

Moreover, since there is a demand for real-time viewing of contentproduced by individuals, which tends to be small in data size, thedecoder first receives the base layer as the highest priority andperforms decoding and reproduction, although this may differ dependingon bandwidth. When the content is reproduced two or more times, such aswhen the decoder receives the enhancement layer during decoding andreproduction of the base layer and loops the reproduction, the decodermay reproduce a high image quality video including the enhancementlayer. If the stream is encoded using such scalable encoding, the videomay be low quality when in an unselected state or at the start of thevideo, but it can offer an experience in which the image quality of thestream progressively increases in an intelligent manner. This is notlimited to just scalable encoding; the same experience can be offered byconfiguring a single stream from a low quality stream reproduced for thefirst time and a second stream encoded using the first stream as areference.

Other Usage Examples

The encoding and decoding may be performed by LSI ex500, which istypically included in each terminal. LSI ex500 may be configured of asingle chip or a plurality of chips. Software for encoding and decodingmoving pictures may be integrated into some type of a recording medium(such as a CD-ROM, a flexible disk, or a hard disk) that is readable by,for example, computer ex111, and the encoding and decoding may beperformed using the software. Furthermore, when smartphone ex115 isequipped with a camera, the video data obtained by the camera may betransmitted. In this case, the video data is coded by LSI ex500 includedin smartphone ex115.

Note that LSI ex500 may be configured to download and activate anapplication. In such a case, the terminal first determines whether it iscompatible with the scheme used to encode the content or whether it iscapable of executing a specific service. When the terminal is notcompatible with the encoding scheme of the content or when the terminalis not capable of executing a specific service, the terminal firstdownloads a codec or application software then obtains and reproducesthe content.

Aside from the example of content providing system ex100 that usesInternet ex101, at least the moving picture encoder (image encoder) orthe moving picture decoder (image decoder) described in the aboveembodiments may be implemented in a digital broadcasting system. Thesame encoding processing and decoding processing may be applied totransmit and receive broadcast radio waves superimposed with multiplexedaudio and video data using, for example, a satellite, even though thisis geared toward multicast whereas unicast is easier with contentproviding system ex100.

[Hardware Configuration]

FIG. 48 illustrates smartphone ex115. FIG. 49 illustrates aconfiguration example of smartphone ex115. Smartphone ex115 includesantenna ex450 for transmitting and receiving radio waves to and frombase station ex110, camera ex465 capable of capturing video and stillimages, and display ex458 that displays decoded data, such as videocaptured by camera ex465 and video received by antenna ex450. Smartphoneex115 further includes user interface ex466 such as a touch panel, audiooutput unit ex457 such as a speaker for outputting speech or otheraudio, audio input unit ex456 such as a microphone for audio input,memory ex467 capable of storing decoded data such as captured video orstill images, recorded audio, received video or still images, and mail,as well as decoded data, and slot ex464 which is an interface for SIMex468 for authorizing access to a network and various data. Note thatexternal memory may be used instead of memory ex467.

Moreover, main controller ex460 which comprehensively controls displayex458 and user interface ex466, power supply circuit ex461, userinterface input controller ex462, video signal processor ex455, camerainterface ex463, display controller ex459, modulator/demodulator ex452,multiplexer/demultiplexer ex453, audio signal processor ex454, slotex464, and memory ex467 are connected via bus ex470.

When the user turns the power button of power supply circuit ex461 on,smartphone ex115 is powered on into an operable state by each componentbeing supplied with power from a battery pack.

Smartphone ex115 performs processing for, for example, calling and datatransmission, based on control performed by main controller ex460, whichincludes a CPU, ROM, and RAM. When making calls, an audio signalrecorded by audio input unit ex456 is converted into a digital audiosignal by audio signal processor ex454, and this is applied with spreadspectrum processing by modulator/demodulator ex452 and digital-analogconversion and frequency conversion processing by transmitter/receiverex451, and then transmitted via antenna ex450. The received data isamplified, frequency converted, and analog-digital converted, inversespread spectrum processed by modulator/demodulator ex452, converted intoan analog audio signal by audio signal processor ex454, and then outputfrom audio output unit ex457. In data transmission mode, text,still-image, or video data is transmitted by main controller ex460 viauser interface input controller ex462 as a result of operation of, forexample, user interface ex466 of the main body, and similar transmissionand reception processing is performed. In data transmission mode, whensending a video, still image, or video and audio, video signal processorex455 compression encodes, via the moving picture encoding methoddescribed in the above embodiments, a video signal stored in memoryex467 or a video signal input from camera ex465, and transmits theencoded video data to multiplexer/demultiplexer ex453. Moreover, audiosignal processor ex454 encodes an audio signal recorded by audio inputunit ex456 while camera ex465 is capturing, for example, a video orstill image, and transmits the encoded audio data tomultiplexer/demultiplexer ex453. Multiplexer/demultiplexer ex453multiplexes the encoded video data and encoded audio data using apredetermined scheme, modulates and converts the data usingmodulator/demodulator (modulator/demodulator circuit) ex452 andtransmitter/receiver ex451, and transmits the result via antenna ex450.

When video appended in an email or a chat, or a video linked from a webpage, for example, is received, in order to decode the multiplexed datareceived via antenna ex450, multiplexer/demultiplexer ex453demultiplexes the multiplexed data to divide the multiplexed data into abitstream of video data and a bitstream of audio data, supplies theencoded video data to video signal processor ex455 via synchronous busex470, and supplies the encoded audio data to audio signal processorex454 via synchronous bus ex470. Video signal processor ex455 decodesthe video signal using a moving picture decoding method corresponding tothe moving picture encoding method described in the above embodiments,and video or a still image included in the linked moving picture file isdisplayed on display ex458 via display controller ex459. Moreover, audiosignal processor ex454 decodes the audio signal and outputs audio fromaudio output unit ex457. Note that since real-time streaming is becomingmore and more popular, there are instances in which reproduction of theaudio may be socially inappropriate depending on the user's environment.Accordingly, as an initial value, a configuration in which only videodata is reproduced, i.e., the audio signal is not reproduced, ispreferable. Audio may be synchronized and reproduced only when an input,such as when the user clicks video data, is received.

Although smartphone ex115 was used in the above example, threeimplementations are conceivable: a transceiver terminal including bothan encoder and a decoder; a transmitter terminal including only anencoder; and a receiver terminal including only a decoder. Further, inthe description of the digital broadcasting system, an example is givenin which multiplexed data obtained as a result of video data beingmultiplexed with, for example, audio data, is received or transmitted,but the multiplexed data may be video data multiplexed with data otherthan audio data, such as text data related to the video. Moreover, thevideo data itself rather than multiplexed data may be received ortransmitted.

Although main controller ex460 including a CPU is described ascontrolling the encoding or decoding processes, terminals often includeGPUs. Accordingly, a configuration is acceptable in which a large areais processed at once by making use of the performance ability of the GPUvia memory shared by the CPU and GPU or memory including an address thatis managed so as to allow common usage by the CPU and GPU. This makes itpossible to shorten encoding time, maintain the real-time nature of thestream, and reduce delay. In particular, processing relating to motionestimation, deblocking filtering, sample adaptive offset (SAO), andtransformation/quantization can be effectively carried out by the GPUinstead of the CPU in units of, for example pictures, all at once.

Although only some exemplary embodiments of the present disclosure havebeen described in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of the present disclosure. Accordingly, all suchmodifications are intended to be included within the scope of thepresent disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to, for example, televisionreceivers, digital video recorders, car navigation systems, mobilephones, digital cameras, digital video cameras, teleconference systems,electronic mirrors, etc.

What is claimed is:
 1. An encoder which encodes image information, theencoder comprising: memory; and circuitry accessible to the memory,wherein the circuitry accessible to the memory: binarizes a data valueindicating the number of non-zero coefficients included in a currentbasic block which is one of one or more basic blocks in a frequencytransform block composed of a plurality of frequency transformcoefficients, according to a conversion table in which a plurality ofdata values and a plurality of binary values are associated with eachother, to encode the image information which includes the data value;and when binarizing the data value, selects the conversion table from aplurality of tables including two or more tables which differ from eachother in difference between a longest bit length and a shortest bitlength of a plurality of binary values associated with the plurality ofdata values, according to a position of the current basic block in thecurrent frequency transform block which is the frequency transform blockincluding the current basic block, and binarizes the data valueaccording to the conversion table selected.
 2. The encoder according toclaim 1, wherein, when selecting the conversion table, the circuitryselects the conversion table according to the number of non-zerocoefficients included in a preceding basic block which is a basic blocklocated before the current basic block in a predetermined scan orderdefined in a descending order of frequencies of the one or more basicblocks in the case where the preceding basic block is present at thesame frequency level as a frequency level at the position of the currentbasic block.
 3. The encoder according to claim 2, wherein, whenselecting the conversion table, the circuitry: selects, as theconversion table, a first table from the plurality of tables when thepreceding basic block is present at the same frequency level and thenumber of non-zero coefficients included in the preceding basic block isa first number; and selects, as the conversion table, a second tablefrom the plurality of tables when the preceding basic block is presentat the same frequency level and the number of non-zero coefficientsincluded in the preceding basic block is a second number larger than thefirst number, the second table having a smaller difference between alongest bit length and a shortest bit length of a plurality of binaryvalues than the first table.
 4. The encoder according to claim 1,wherein, when selecting the conversion table, the circuitry selects,from the plurality of tables, the conversion table which has a smallerdifference between a longest bit length and a shortest bit length of aplurality of binary values than a predetermined difference, in the casewhere (i) a preceding basic block which is a basic block located beforethe current basic block in a predetermined scan order defined in adescending order of frequencies of the one or more basic blocks is notpresent at the same frequency level as a frequency level at the positionof the current basic block and (ii) a specific basic block which is abasic block including a non-zero coefficient first in the predeterminedscan order is present at a frequency level higher than the frequencylevel at the position of the current basic block.
 5. The encoderaccording to claim 4, wherein, when selecting the conversion table, thecircuitry selects the conversion table which has a smallest differencebetween a longest bit length and a shortest bit length of a plurality ofbinary values from the plurality of tables when the preceding basicblock is not present at the same frequency level and the specific basicblock is present at the frequency level higher than the frequency levelat the position of the current basic block.
 6. The encoder according toclaim 1, wherein, when selecting the conversion table, the circuitryselects the conversion table according to the number of non-zerocoefficients estimated to be the number of non-zero coefficientsincluded in the current basic block based on a neighboring frequencytransform block which is a frequency transform block located around thecurrent frequency transform block, in the case where (i) a precedingbasic block which is a basic block located before the current basicblock in a predetermined scan order defined in a descending order offrequencies of the one or more basic blocks is not present at the samefrequency level as a frequency level at the position of the currentbasic block and (ii) a specific basic block which is a basic blockincluding a non-zero coefficient first in the predetermined scan orderis not present at a frequency level higher than a frequency level at aposition of the current basic block.
 7. The encoder according to claim6, wherein, when selecting the conversion table, the circuitry: selectsa first table as the conversion table from the plurality of tables, when(i) the preceding basic block is not present at the same frequencylevel, (ii) the specific basic block is not present at the higherfrequency level, and (iii) the number of non-zero coefficients estimatedto be the number of non-zero coefficients based on the neighboringfrequency transform block is a first number; and selects a second tablewhich has a smaller difference between a longest bit length and ashortest bit length of a plurality of binary values than the first tableas the conversion table from the plurality of tables, when (i) thepreceding basic block is not present at the same frequency level, (ii)the specific basic block is not present at the higher frequency level,and (iii) the number of non-zero coefficients estimated to be the numberof non-zero coefficients based on the neighboring frequency transformblock is a second number larger than the first number.
 8. The encoderaccording to claim 6, wherein the neighboring frequency transform blockis one of (i) a frequency transform block adjacent to a left of or abovethe current frequency transform block, (ii) a frequency transform blockwhich has been encoded immediately before the current frequencytransform block, and (iii) a frequency transform block which is locatedwithin a predetermined range from the current frequency transform blockand is the same as the current frequency transform block in coding mode,the coding mode being one of an inter prediction mode and an intraprediction mode.
 9. The encoder according to claim 6, wherein the numberof non-zero coefficients estimated based on the neighboring frequencytransform block is estimated based on one of (i) the number of non-zerocoefficients included in a basic block which is one of the one or morebasic blocks in the neighboring frequency transform block and whoseposition relative to the neighboring frequency transform block isequivalent to a position of the current basic block relative to thecurrent frequency transform block and (ii) the number of non-zerocoefficients included in an entirety of the neighboring frequencytransform block.
 10. The encoder according to claim 1, wherein, whenselecting the conversion table, the circuitry selects the conversiontable according to whether a coding mode of the current basic block isan inter prediction mode or an intra prediction mode, in the case where(i) a preceding basic block which is a basic block located before thecurrent basic block in a predetermined scan order defined in adescending order of frequencies of the one or more basic blocks is notpresent at the same frequency level as a frequency level at the positionof the current basic block and (ii) a specific basic block which is abasic block including a non-zero coefficient first in the predeterminedscan order is not present at a frequency level higher than a frequencylevel at the position of the current basic block.
 11. The encoderaccording to claim 10, wherein, when selecting the conversion table, thecircuitry: selects, as the conversion table, a first table from theplurality of tables when (i) the preceding basic block is not present atthe same frequency level, (ii) the specific basic block is not presentat the higher level, and (iii) the coding mode of the current basicblock is an inter prediction mode; and selects, as the conversion table,a second table from the plurality of tables when (i) the preceding basicblock is not present at the same frequency level, (ii) the specificbasic block is not present at the higher level, and (iii) the codingmode for the current basic block is an intra prediction mode, the secondtable having a smaller difference between a longest bit length and ashortest bit length of a plurality of binary values than the firsttable.
 12. The encoder according to claim 1, wherein, when selecting theconversion table, the circuitry selects the conversion table accordingto a quantization parameter which is used to encode the current basicblock, in the case where (i) a preceding basic block which is a basicblock located before the current basic block in a predetermined scanorder defined in a descending order of frequencies of the one or morebasic blocks is not present at the same frequency level as a frequencylevel at the position of the current basic block and (ii) a specificbasic block which is a basic block including a non-zero coefficientfirst in the predetermined scan order is not present at a frequencylevel higher than a frequency level at the position of the current basicblock.
 13. The encoder according to claim 12, wherein, when selectingthe conversion table, the circuitry: selects a first table as theconversion table from the plurality of tables, when (i) the precedingbasic block is not present at the same frequency level, (ii) thespecific basic block is not present at the higher frequency level, and(iii) the quantization parameter is a first value; and selects a secondtable which has a smaller difference than the first table as theconversion table from the plurality of tables, when (i) the precedingbasic block is not present at the same frequency level, (ii) thespecific basic block is not present at the higher frequency level, and(iii) the quantization parameter is a second value smaller than thefirst value, the second table having a smaller difference between alongest bit length and a shortest bit length of a plurality of binaryvalues than the first table.
 14. The encoder according to claim 1,wherein the circuitry: encodes the image information, and outputs abitstream in which the image information has been encoded; when encodingthe image information and outputting the bitstream; binarizes the imageinformation; switches whether or not to apply arithmetic encoding to abinary data string in which the image information has been binarized;when arithmetic encoding is applied to the binary data string, appliesarithmetic encoding to the binary data string, and outputs the bitstreamwhich includes the binary data string to which arithmetic encoding hasbeen applied; and when arithmetic encoding is not applied to the binarydata string, skips applying arithmetic encoding to the binary datastring and outputs the bitstream which includes the binary data stringto which arithmetic encoding has not been applied, and when binarizingthe image information, binarizes frequency transform coefficientinformation which is related to frequency components of an image andincluded in the image information, according to different binarizationformats between when arithmetic encoding is applied to the binary datastring and when arithmetic encoding is not applied to the binary datastring; when binarizing the image information, binarizes a part or anentirety of prediction parameter information which is related toprediction methods of an image and included in the image information,according to a common binarization format between when arithmeticencoding is applied to the binary data string and when arithmeticencoding is not applied to the binary data string; and when binarizingthe frequency transform coefficient information in the case wherearithmetic encoding is not applied to the binary data string, binarizesthe data value included in the frequency transform coefficientinformation, according to the conversion table selected from theplurality of tables based on the position of the current basic block.15. A decoder which decodes image information, the decoder comprising:memory; and circuitry accessible to the memory, wherein the circuitryaccessible to the memory: inverse binarizes a binary value which hasbeen obtained by binarizing a data value, according to a conversiontable in which a plurality of data values and a plurality of binaryvalues are associated with each other, to decode the image informationwhich includes the data value, the data value indicating the number ofnon-zero coefficients included in a current basic block which is one ofone or more basic blocks in a frequency transform block composed of aplurality of frequency transform coefficients; and when inversebinarizing the binary value, selects the conversion table from aplurality of tables including two or more tables which differ from eachother in difference between a longest bit length and a shortest bitlength of a plurality of binary values associated with the plurality ofdata values, according to a position of the current basic block in thecurrent frequency transform block which is the frequency transform blockincluding the current basic block, and inverse binarizes the binaryvalue according to the conversion table selected.
 16. The decoderaccording to claim 15, wherein, when selecting the conversion table, thecircuitry selects the conversion table according to the number ofnon-zero coefficients included in a preceding basic block which is abasic block located before the current basic block in a predeterminedscan order defined in a descending order of frequencies of the one ormore basic blocks in the case where the preceding basic block is presentat the same frequency level as a frequency level at the position of thecurrent basic block.
 17. The decoder according to claim 16, wherein,when selecting the conversion table, the circuitry: selects, as theconversion table, a first table from the plurality of tables when thepreceding basic block is present at the same frequency level and thenumber of non-zero coefficients included in the preceding basic block isa first number; and selects, as the conversion table, a second tablefrom the plurality of tables when the preceding basic block is presentat the same frequency level and the number of non-zero coefficientsincluded in the preceding basic block is a second number larger than thefirst number, the second table having a smaller difference between alongest bit length and a shortest bit length of a plurality of binaryvalues than the first table.
 18. The decoder according to claim 15,wherein, when selecting the conversion table, the circuitry selects,from the plurality of tables, the conversion table which has a smallerdifference between a longest bit length and a shortest bit length of aplurality of binary values than a predetermined difference, in the casewhere (i) a preceding basic block which is a basic block located beforethe current basic block in a predetermined scan order defined in adescending order of frequencies of the one or more basic blocks is notpresent at the same frequency level as a frequency level at the positionof the current basic block and (ii) a specific basic block which is abasic block including a non-zero coefficient first in the predeterminedscan order is present at a frequency level higher than the frequencylevel at the position of the current basic block.
 19. The decoderaccording to claim 18, wherein, when selecting the conversion table, thecircuitry selects the conversion table which has a smallest differencebetween a longest bit length and a shortest bit length of a plurality ofbinary values from the plurality of tables when the preceding basicblock is not present at the same frequency level and the specific basicblock is present at the frequency level higher than the frequency levelat the position of the current basic block.
 20. The decoder according toclaim 15, wherein, when selecting the conversion table, the circuitryselects the conversion table according to the number of non-zerocoefficients estimated to be the number of non-zero coefficientsincluded in the current basic block based on a neighboring frequencytransform block which is a frequency transform block located around thecurrent frequency transform block, in the case where (i) a precedingbasic block which is a basic block located before the current basicblock in a predetermined scan order defined in a descending order offrequencies of the one or more basic blocks is not present at the samefrequency level as a frequency level at the position of the currentbasic block and (ii) a specific basic block which is a basic blockincluding a non-zero coefficient first in the predetermined scan orderis not present at a frequency level higher than a frequency level at aposition of the current basic block.
 21. The decoder according to claim20, wherein, when selecting the conversion table, the circuitry: selectsa first table as the conversion table from the plurality of tables, when(i) the preceding basic block is not present at the same frequencylevel, (ii) the specific basic block is not present at the higherfrequency level, and (iii) the number of non-zero coefficients estimatedto be the number of non-zero coefficients based on the neighboringfrequency transform block is a first number; and selects a second tablewhich has a smaller difference between a longest bit length and ashortest bit length of a plurality of binary values than the first tableas the conversion table from the plurality of tables, when (i) thepreceding basic block is not present at the same frequency level, (ii)the specific basic block is not present at the higher frequency level,and (iii) the number of non-zero coefficients estimated to be the numberof non-zero coefficients based on the neighboring frequency transformblock is a second number larger than the first number.
 22. The decoderaccording to claim 20, wherein the neighboring frequency transform blockis one of (i) a frequency transform block adjacent to a left of or abovethe current frequency transform block, (ii) a frequency transform blockwhich has been encoded immediately before the current frequencytransform block, and (iii) a frequency transform block which is locatedwithin a predetermined range from the current frequency transform blockand is the same as the current frequency transform block in coding mode,the coding mode being one of an inter prediction mode and an intraprediction mode.
 23. The decoder according to claim 20, wherein thenumber of non-zero coefficients estimated based on the neighboringfrequency transform block is estimated based on one of (i) the number ofnon-zero coefficients included in a basic block which is one of the oneor more basic blocks in the neighboring frequency transform block andwhose position relative to the neighboring frequency transform block isequivalent to a position of the current basic block relative to thecurrent frequency transform block and (ii) the number of non-zerocoefficients included in an entirety of the neighboring frequencytransform block.
 24. The decoder according to claim 15, wherein, whenselecting the conversion table, the circuitry selects the conversiontable according to whether a coding mode of the current basic block isan inter prediction mode or an intra prediction mode, in the case where(i) a preceding basic block which is a basic block located before thecurrent basic block in a predetermined scan order defined in adescending order of frequencies of the one or more basic blocks is notpresent at the same frequency level as a frequency level at the positionof the current basic block and (ii) a specific basic block which is abasic block including a non-zero coefficient first in the predeterminedscan order is not present at a frequency level higher than a frequencylevel at the position of the current basic block.
 25. The decoderaccording to claim 24, wherein, when selecting the conversion table, thecircuitry: selects, as the conversion table, a first table from theplurality of tables when (i) the preceding basic block is not present atthe same frequency level, (ii) the specific basic block is not presentat the higher level, and (iii) the coding mode of the current basicblock is an inter prediction mode; and selects, as the conversion table,a second table from the plurality of tables when (i) the preceding basicblock is not present at the same frequency level, (ii) the specificbasic block is not present at the higher level, and (iii) the codingmode for the current basic block is an intra prediction mode, the secondtable having a smaller difference between a longest bit length and ashortest bit length of a plurality of binary values than the firsttable.
 26. The decoder according to claim 15, wherein, when selectingthe conversion table, the circuitry selects the conversion tableaccording to a quantization parameter which is used to encode thecurrent basic block, in the case where (i) a preceding basic block whichis a basic block located before the current basic block in apredetermined scan order defined in a descending order of frequencies ofthe one or more basic blocks is not present at the same frequency levelas a frequency level at the position of the current basic block and (ii)a specific basic block which is a basic block including a non-zerocoefficient first in the predetermined scan order is not present at afrequency level higher than a frequency level at the position of thecurrent basic block.
 27. The decoder according to claim 26, wherein,when selecting the conversion table, the circuitry: selects a firsttable as the conversion table from the plurality of tables, when (i) thepreceding basic block is not present at the same frequency level, (ii)the specific basic block is not present at the higher frequency level,and (iii) the quantization parameter is a first value; and selects asecond table which has a smaller difference than the first table as theconversion table from the plurality of tables, when (i) the precedingbasic block is not present at the same frequency level, (ii) thespecific basic block is not present at the higher frequency level, and(iii) the quantization parameter is a second value smaller than thefirst value, the second table having a smaller difference between alongest bit length and a shortest bit length of a plurality of binaryvalues than the first table.
 28. The decoder according to claim 15,wherein the circuitry: obtains a bitstream in which the imageinformation has been encoded, and decodes the image information; whenobtaining the bitstream and decoding the image information: obtains thebitstream which includes a binary data string in which the imageinformation has been binarized; switches whether or not to applyarithmetic decoding to the binary data string which is included in thebitstream; when arithmetic decoding is applied to the binary datastring, applies arithmetic decoding to the binary data string, andinverse binarizes the binary data string to which arithmetic decodinghas been applied, to decode the image information; and when arithmeticdecoding is not applied to the binary data string, skips applyingarithmetic decoding to the binary data string, and inverse binarizes thebinary data string to which arithmetic decoding has not been applied, todecode the image information; when inverse binarizing the binary datastring, inverse binarizes a first portion which is included in thebinary data string and in which frequency transform coefficientinformation related to frequency components of an image has beenbinarized, according to different inverse binarization formats betweenwhen arithmetic decoding is applied to the binary data string and whenarithmetic decoding is not applied to the binary data string; wheninverse binarizing the binary data string, inverse binarizes a secondportion which is included in the binary data string and in which a partor an entirety of prediction parameter information related to predictionmethods of the image has been binarized, according to a common inversebinarization format between when arithmetic decoding is applied to thebinary data string and when arithmetic decoding is not applied to thebinary data string; and when inverse binarizing the first portion in thecase where arithmetic decoding is not applied to the binary data string,inverse binarizes the binary value included in the first portion,according to the conversion table selected from the plurality of tablesbased on a position of the current basic block.
 29. An encoding methodfor encoding image information, the encoding method comprising:binarizing a data value indicating the number of non-zero coefficientsincluded in a current basic block which is one of one or more basicblocks in a frequency transform block composed of a plurality offrequency transform coefficients, according to a conversion table inwhich a plurality of data values and a plurality of binary values areassociated with each other, to encode the image information whichincludes the data value; and in the binarizing of the data value,selecting the conversion table from a plurality of tables including twoor more tables which differ from each other in difference between alongest bit length and a shortest bit length of a plurality of binaryvalues associated with the plurality of data values, according to aposition of the current basic block in the current frequency transformblock which is the frequency transform block including the current basicblock, and binarizing the data value according to the conversion tableselected.
 30. A decoding method for decoding image information, thedecoding method comprising: inverse binarizing a binary value which hasbeen obtained by binarizing a data value, according to a conversiontable in which a plurality of data values and a plurality of binaryvalues are associated with each other, to decode the image informationwhich includes the data value, the data value indicating the number ofnon-zero coefficients included in a current basic block which is one ofone or more basic blocks in a frequency transform block composed of aplurality of frequency transform coefficients; and in the inversebinarizing of the binary value, selecting the conversion table from aplurality of tables including two or more tables which differ from eachother in difference between a longest bit length and a shortest bitlength of a plurality of binary values associated with the plurality ofdata values, according to a position of the current basic block in thecurrent frequency transform block which is the frequency transform blockincluding the current basic block, and inverse binarizing the binaryvalue according to the conversion table selected.